LegionCore with playerbot embedding

1. Fix bugs yourself if you like it.

Known bugs:

1. playerbots don't find path in BG aggressively, just passive now.
2. db is lack except playerbot part. you can import a default db version.
3. BotGroupAI work not completely.

Known fix done:

1. playerbots join arena opcode need be implemented.
2. db sql involved playerbot.
3. common.lib for vmap collision calculation.

Known settings:

1. playerbot max count set to 10 in bot mgr
2. playerbot account prefix is PLAYERBOT