PlaceholderAPI and Legacy colors support

PlaceholderAPI support

Added support for placeholders from PlaceholderAPI. These placeholders can be used in conjunction with those of the plugin, it is suggested to use those of the same plugin in case there are similar placeholders.

Legacy color support

Basic support for color codes &1, &2, &l, &k, etc... has been added.
These colors will be converted to their MiniMessage equivalent before being sent.