Fix strict standards warnings.
Add 'meta_tables' parameter in setup_globals() method.

This fixes issues in BP 2.0 utilizing the WP metadata API to access
groupmeta calls.
Add a third argument - $args - to BP_Groups_Hierarchy class.

Specifically, the most important parts of this commit is the addition
of the 'populate_extras' parameter to fetch extra group data during
initialization.

This mirrors the following BuddyPress changesets:
- https://buddypress.trac.wordpress.org/changeset/7934
- https://buddypress.trac.wordpress.org/changeset/8056
- https://buddypress.trac.wordpress.org/changeset/8056

Fixes issues with extra group data not being populated at runtime in
BP Group Hierarchy.
Fix 'already defined constructor' strict standards warning.
Add 'populate_extras' parameter in bp_group_hierarchy_override_template().

Fixes problems with the group extras not populating in the group
directory.

See commit 17ff2f7.
Merge pull request #7 from r-a-y/2.0-fixes

BP 2.0 fixes