feature(file): display file upload limit on file upload form

Refs #6355
Merge pull request #6876 from Elgg/1.9

Merge 1.9 to 1.x
Merge branch '1.x'
Merge pull request #6930 from Elgg/1.9

Merge 1.9 up to 1.x
chore(docs): Point INSTALL.txt to learn.elgg.org

Don't want to have to keep these two versions of instructions in sync.
feature(requirements): PHP 5.3.3+ is now required

Symfony needs 5.3.3 and we plan on using their components heavily.

Closes #6165
Merge pull request #6926 from ewinslow/php-53-b6165

Require PHP 5.3.3+ to run Elgg
perf(session): speed up elgg_is_admin_user()

This function currently makes one query and generally hits the query cache
several more times. This generally eliminates the query and avoids the overhead
of the DB service. If a query must be done we use a minimal result set.
Merge pull request #6947 from mrclay/is_admin_user

perf(session): speed up elgg_is_admin_user()
Merge branch '1.9' of http://github.com/Elgg/Elgg into 1.x

Conflicts:
	composer.json
Merge pull request #6972 from THINKGlobalSchool/display-file-upload-limit

feature(file): display file upload limit on file upload form
Merge pull request #7029 from Elgg/1.9

Merge 1.9 up to 1.x
Merge pull request #7030 from Elgg/1.x

Merge 1.x up to master