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

Refs #6355
feature(groups): Added featured groups as a tab along with groups, popular, discussions

Slightly changed and combined work of @thuvalpakshi
Merge pull request #6876 from Elgg/1.9

Merge 1.9 to 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
fix(config): path is derived from PHP, not database

Elgg falls apart if `$CONFIG->path` is set to anything but the Elgg root,
so there is no point in saving a different value to the DB
or in respecting any value already saved to the DB.

Refs #2316
chore(composer): add more detailed requirements to composer.json
chore(composer): Ran composer update
Merge pull request #7068 from ewinslow/composer

chore(composer): add more detailed requirements to composer.json
Merge pull request #7069 from ewinslow/config-b2316

fix(config): path is derived from PHP, not database
chore(composer): Rely on composer autoloader to load core classes
chore(travis): run tests on PHP 5.3.3 and 5.6

5.3.3 is the lowest supported version, so we should test explicitly on that.

PHP 5.6 isn't stable yet, but we want to be ready for it.
Merge pull request #7082 from Elgg/1.9

Merge 1.9 up to 1.x