- Implemented advanced hook management

Hook management

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Hooks can be managed in similar way to this used in .hgrc files.

To access hooks setting click `advanced setup` on Hooks section of Mercurial

Settings in Admin. 

There are 4 built in hooks that cannot be changed (only enable/disable by

checkboxes on previos section).

To add another custom hook simply fill in first section with 

<name>.<hook_type> and the second one with hook path. Example hooks

can be found at *rhodecode.lib.hooks*.