plugin text commands: refactoring, text now only contain main commands, and other plugin can add commands themselve:

- registerTextCommands can be called by a plugin in its __init__ method, it looks for methods starting with "cmd_" and register them as new commands
    - addWhoIsCb: add a callback to /whois command, the callback can complete whois informations
    - plugins parrot, XEP-0045 and XEP-0092 now manage their own commands

src/core/constants.py

@@ -36,3 +36,6 @@ class Const(object):
     PROF_KEY_NONE = '@NONE@'
     PROF_KEY_DEFAULT = '@DEFAULT@'
     IQ_SET = '/iq[@type="set"]'
+
+    # names of widely used plugins
+    TEXT_CMDS = 'TEXT-COMMANDS'