Command Conditions and MANY other code changes for Generics <3🌮

This completes and fully enables a new feature called "Conditions"

We already had some forms of conditions built into @Flags such as
on the Player for itemheld.

However, letting end users add additional restrictions to existing context
handlers such as players is not possible without redefining the context.

That's not friendly nor scalable.

Flags will now be primarily only for controlling how to resolve a context,
and then Conditions will then be the way to validate the context and trigger
a failure if the condition is not met.

Conditions can be placed on Command Class, Methods, or individual Parameters.

example/src/main/java/co/aikar/acfexample/ACFExample.java

@@ -24,6 +24,7 @@
 package co.aikar.acfexample;
 
 import co.aikar.commands.BukkitCommandManager;
+import co.aikar.commands.ConditionFailedException;
 import co.aikar.commands.MessageKeys;
 import co.aikar.commands.MessageType;
 import com.google.common.collect.Lists;
@@ -64,17 +65,31 @@ public final class ACFExample extends JavaPlugin {
             Lists.newArrayList("foo", "bar", "baz")
         ));
 
-        // 5: Register your commands - This first command demonstrates adding an exception handler to that command
+        // 5: Register Command Conditions
+        commandManager.getCommandConditions().addCondition(SomeObject.class, "limits", (c, exec, value) -> {
+            if (value == null) {
+                return true;
+            }
+            if (c.hasConfig("min") && c.getConfigValue("min", 0) > value.getValue()) {
+                throw new ConditionFailedException("Min value must be " + c.getConfigValue("min", 0));
+            }
+            if (c.hasConfig("max") && c.getConfigValue("max", 3) < value.getValue()) {
+                throw new ConditionFailedException("Max value must be " + c.getConfigValue("max", 3));
+            }
+            return true;
+        });
+
+        // 6: Register your commands - This first command demonstrates adding an exception handler to that command
         commandManager.registerCommand(new SomeCommand().setExceptionHandler((command, registeredCommand, sender, args, t) -> {
                 sender.sendMessage(MessageType.ERROR, MessageKeys.ERROR_GENERIC_LOGGED);
                 return true; // mark as handeled, default message will not be send to sender
         }));
-        // 5: Register an additional command. This one happens to share the same CommandAlias as the previous command
+        // 7: Register an additional command. This one happens to share the same CommandAlias as the previous command
         // This means it simply registers additional sub commands under the same command, but organized into separate
         // Classes (Maybe different permission sets)
         commandManager.registerCommand(new SomeCommand_ExtraSubs());
 
-        // 6: Register default exception handler for any command that doesn't supply its own
+        // 8: Register default exception handler for any command that doesn't supply its own
         commandManager.setDefaultExceptionHandler((command, registeredCommand, sender, args, t) -> {
             getLogger().warning("Error occured while executing command " + command.getName());
             return false; // mark as unhandeled, sender will see default message