Don't allow BuddyPress Docs to run theme compatibility mode

cbox-theme provides its own templates for Docs, for the moment at least.

See boonebgorges/buddypress-docs#328
Tweak templates for BP Docs Wiki.
Fix 'New Topic' button for group forums.

bp_is_group_forum() changed in BP 1.7 to check if the legacy forums are
are explicitly installed.  This change broke the visibility of the
button when using the bbPress plugin.

In this commit, we use a customized version of bp_is_group_forum() to
do our group forum check.  Doing this ensures that the 'New Topic'
button will be displayed again when on group forum page.

Fixes #147.
Add missing .php extension to group request membership template.
In Recent Blog Posts widget, do not assume what the site directory is.

Use native BP function - bp_blogs_directory_permalink() - to output the
correct site directory link.

Props @christianwach.  Fixes #153.
fix second level menu visibility as raised in issue 121
Merge pull request #154 from christianwach/master

Fix visibility of second level menus props @christianwach