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
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
Merge pull request #6332 from mrclay/5920

Fixes #5920: Returns 1.8 behavior of ElggEntity->subtype read
fix(developer_tools): Added all of the defined icons to the theme preview.
fixes(site_notifications): Using the alert icon for notices.

Fixes #6447
chore(scrutinizer): Updated scrutinizer to ignore */vendor/*
fix(views): Using sitedescription in meta description tag.

fixes #3973
Merge pull request #6330 from mrclay/6204

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
test(groups): page owner is not an entity when running SimpleTest

Fixes #6472
Merge pull request #6474 from hypeJunction/group_acl_test

test(groups): page owner is not an entity when running SimpleTest