Templates: Better support for custom mapleaders.

- Added 'mmtemplates#core#SetMapleader' and 'mmtemplates#core#ResetMapleader'.
- Search for cursor and jump tags works independently of editor settings.
Latex-Support: Better support for custom mapleaders.

- Added 'Latex_SetMapLeader' and 'Latex_ResetMapLeader'.
- Improved setting and resetting of maplocalleader in filetype plug-in.
Perl-Support: Fixed support for custom mapleaders.

- Added 'Perl_SetMapLeader' and 'Perl_ResetMapLeader'.
- Fixed setting and resetting of maplocalleader in filetype plug-ins.
C-Support: Fixed support for custom mapleaders.

- Added 'C_SetMapLeader' and 'C_ResetMapLeader'.
- Fixed setting and resetting of maplocalleader in filetype plug-ins.
Merge remote-tracking branch 'upstream/master'