fix(invitefriends): check if registration is allowed before display menu item and pages

Refs #6356
Fixes #6400
chore(invitefriends): form labels

Format labels according to #6356, adds email label and moves instructions into its own div, removes leading spaces in email notifications

Refs #6400
fix(invitefriends): make invite form sticky
chore(invitefriends): use p tag instead of div for instructions
Merge pull request #6401 from hypeJunction/invitefriends

fix(invitefriends): check if registration is allowed before displaying...
fix(routing): URL-decodes path segments like Elgg 1.8

Non-ASCII characters get URL encoded in $_SERVER['PATH_INFO'] so instead we
copy the URL path into a query string var and use that var to build path
segments in the router. This should yield identical behavior as Elgg 1.8.

Fixes #6218
fix(http): makes HTTP request/parameter bag PHP 5.2 compatible

The original Symfony versions use array_replace. We use array_merge, which
is identical for the purpose it's used.
test(groups): corrects tests for groups write access hook

If an admin user is logged in, all permissions tests pass, even if
we're testing whether a non-admin user has access to something. This
turns on access control for the test.
test(routing): adds more comprehensive tests for router

This tests that the router passes the URL segments and original
identifier to the page handler, and that a URL-encoded segment
is properly decoded.
Merge pull request #6440 from mrclay/hypeJunction-group_acl_test

Write access array in group context should contain that groups acl
fix(site_notifications): added correct key for menu item
fix(upgrade): Setting time_updated and last_action for migrated comment and discussion entities.

Fixes #6395.
fix(css): Added CSS for elgg-state-selected menu items in theme sandbox.
fix(ui): Added CSS to make the site menu show up correctly in theme sandbox.
Merge pull request #6441 from PerJensen/master

fix(site_notifications): added correct key, link_class, for menu item
docs(updates): Updating contributing docs to point to feedback and planning group and to mention the commit message format.
docs(fix): Fixing MD links for new docs.
Merge pull request #6444 from brettp/6395

fix(upgrade): Setting time_updated and last_action for migrated comment ...

LGTM
Merge pull request #6439 from mrclay/6218

fix(routing): URL-decodes path segments like Elgg 1.8
test(groups): fix parameter passed to elgg_set_page_owner_guid()

Passing correct value: guid instead of the entity