[entropy.core.settings.base] add support for disabled repository ini files

Together with the "enabled=" repository configuration option inside repository
configuration files, the same ones can be in a disabled state if they are prefixed
with "_<file prefix>" (where <file prefix> is entropy_ at this time).
[entropy.server] RepositoryConfigParser: add repository add, remove methods
[eit] main: do not execute command if not allowed
[equo] fix "equo repo add" arguments parsing, catch AttributeError during arguments validation
[entropy.server.interfaces] export RepositoryConfigParser
[entropy.server] RepositoryConfigParser: make possible to leave the base= parameter unset
[equo] equo repo add: uniform strings, s/repository identifier/repository name/
[client] update entropy.pot
[client] po: update translations
[eit] add "eit repo add" and "eit repo remove" commands (and move "eit repo" to "eit repo show")
[server] update entropy-server.pot
[server] po: update translations
Release Entropy 189
Tagging Entropy version 189
[eit.commands.log] fix bzless path, bzless moved from /bin to /usr/bin