Add IgnoreGroup support

[rmarquis]

Unlike what I previously thought, some AUR packages have groups (f.e. kodi-addon-pvr-hts is part of kodi-addons group). This information is correctly displayed in the AUR interface, thus it should be handle by pacaur.

Add support for the related IgnoreGroup option.

To do:

• patch cower to retrieve the Groups array from the RPC (done)
• implement Groups display in the --info package info view (0c344db)
• implement check for AUR targets that that are part of an IgnoreGroup (87c15c2)
• implement check for AUR packages dependencies that that are part of an IgnoreGroup (c8f96c0)
• implement check for binary packages dependencies that are part of an IgnoreGroup (8c1dabb)
• check multi-group implementation (package that belongs to more than a group) (2130f83)
• ensure local package take IgnoreGroup into account when upgrading (8e474b4)

This incidentally overrides the previous decision in #501.
See also #267 as an extra error can be easily trigerred by IgnoreGroup prompt.

[ismaelgv]

I'll backport these changes to pacaur 5.0 when the whole issue is completed.

[rmarquis]

Done in above mentionned commits.

[ismaelgv]

Backport completed and GetIgnoredGrps() documented.