change xlrstats configuration from xml format to ini

- move xlrstats.xml to plugin_xmlrstats.ini
- use ini style in tests

Upgrade safe. Old xlrstats.xml configuration can be used.
small improvements in the help text
small improvements in the help text
use group names for command levels and extent help text
fix group name
allow configurable !xlrstats message
allow configurable !xlrtopstats message
templates: change xlrstats.xml to plaugin_xmlstats.ini
Merge pull request #138 from ozon/improvements/plugin_xlrstats

[xlrstats] change configuration format from xml format to ini and other improvements:
- !xlrstats and !xlrtopstats messages can be customized
- config file accepts group names for commands