[12415] Avoid creature not respawning when not looted.

This occurs when corpse decay time is bigger than respawn time.
This is not blizzlike, to permit a creature respawn when its corpse still exist we need a complete rewrite of creature pool system.

Fix cmangos/mangos-wotlk#72
[12416] Implement spells 53035, 53036 and 53037

This will properly handle the periodic dummy auras and will also add stacking exception

Used in Azjol-Nerub for Hadronox encounter
[12417] Add negative exception for spells 57508 - 57512

Close #106 because it's invalid
[12418] Fix possible crash due to [12409]

Thanks Schmoozerd for pointing
[12419] Implement spell 56072

Also add caster exception for spell 56505
[12420] Add support for XP-Gain disabling

Add CONDITION_XP_USER to be able to check if a player has XP-Gain enabled or disabled
Add SCRIPT_COMMAND_XP_USER to enable/disable XP-Gain for a player

Signed-off-by: Schmoozerd <schmoozerd@scriptdev2.com>
[12421] Implement CONDITION_GENDER Thanks to crackm for testing
[12422] Add helper script to easily create a topic branch
[12423] Add a helper script to easily merge topic branches and pull-requests
[12424] Add Contributing Guidelines

[ci skip]
[12425] We centralized our issue tracking on cmangos/issues

All existing issues have been migrated to this centralized repository. As
of now, we will deactive the issue tracker on this repository and only use
the new central one.
Please note that Pull Requests are still on the repository containing the
code and you'll still post them there, as they are directly associated
with that code.

Thanks to @github for making this possible with
https://github.com/blog/1439-closing-issues-across-repositories

[ci skip]