fix(entities): reverts to 1.8 behavior of ElggEntity->subtype reads

The subtype property was never properly implemented to return the string subtype
but rather returned the integer ID of the subtype. Although this was "fixed" before
this commit, it was decided that it was dangerous to start returning strings where
older plugins might be expecting integers. This deprecates reads of the property
altogether (encouraging the use of getSubtype()) and otherwise returns the behavior
of the property in Elgg 1.8.

Fixes #5920
perf(upgrade): speeds up migrating remember me codes

The Remember me cookie implementation has been improved by moving codes
to a separate table. This performs that migration in one query.

Fixes #6204
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(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.
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
Merge pull request #6462 from hypeJunction/group_acl_test

test(groups): fix parameter passed to elgg_set_page_owner_guid()
perf(groups): remove redundant filter of user-owner group acls

Since 1.8 upgrade the iteration to filter out acls that define group membership and are owned by the user are redundant

Fixes #6434
fix(ui): use correct logo in favicon

Fixes #6446
feature(ui): add svg favicon

Adds svg favicon

Refs #5445
feature(ui): adds fallback png favicons

Adds png fallback favicons

Refs #5445
Merge pull request #6466 from hypeJunction/favicon

Fixes favicon color, adds svg favicon