Add group ID as filter argument

The group id would be helpful to have when filtering the setting values
in BP_Docs_Group_Extension::enable_at_group_creation().
Don't use $_POST['doc_id'] as existing post ID if it's 0

Fixes #411

Props @original-brownbear
Readme
pot update for 1.7.1
Bump version numbers to 1.7.1
When a edit/create POST submit fails, use failed values when rerendering page

This should help prevent lost values

Fixes #404
Readme
Only add the group slug to Create New Doc links if current user can associate with group

This prevents the 'Create New Doc' link from containing the group slug in the
Howdy dropdown menu.

Fixes #413
Better handling of Doc comment protection based on Doc settings

Fixes #405
Whitespace
Readme
Move to 1.8 branch
Remove unused function
Remove inline JS for meta box toggles and do everything with no-js CSS classes

Fixes #415
Implementation of map_meta_caps for BP Docs custom capabilities

This will be the basis of a refactor of these capabilities to use current_user_can()
rather than bp_docs_current_user_can(), allowing for better testability
More bp_docs_associate_with_group permissions tests
Improved behavior when bouncing from viewing the Edit tab
Don't wipe out all non-bp_docs caps
Use current_user_can() to build bp_docs_doc_action_links()
Use current_user_can() when building Create New Doc button