chore(input): Pull `get_input` and `set_input` into an OO service

Also adds test stubs to be implemented when the global state is removed.

Fixes #7091
Merge pull request #7433 from ewinslow/oo-input

chore(input): Pull `get_input` and `set_input` into an OO service
chore(cache): Move simplecache and system cache into OO services
chore(datalist): Move datalist_* apis into an OO service
deprecate(libraries): End support for `elgg_register_library` and `elgg_load_library`

Class autoloading is better in every way. It's trivial to use static methods
on autoloaded classes rather than `elgg_*_library` with global functions.

This is a "soft" deprecation (no warnings/notices when using the deprecated APIs)
because we're not updating core plugins just yet.
chore(assets): Move external files structure and logic to OO service
Merge pull request #7441 from ewinslow/oo-datalist

chore(datalist): Move datalist_* apis into an OO service
Merge pull request #7443 from ewinslow/deprecate-libraries

deprecate(libraries): End support for `elgg_register_library` and `elgg_load_library`
Merge pull request #7439 from ewinslow/oo-cache

chore(cache): Move simplecache and system cache into OO services
Merge pull request #7444 from ewinslow/oo-external-files

chore(assets): Move external files structure and logic to OO service
chore(travis): Fix coding violation in SimpleCache that slipped through
Merge pull request #7446 from ewinslow/fix-travis-build

chore(travis): Fix coding violation in SimpleCache that slipped through
chore(config): Move high-level elgg_*_config apis into OO service
deprecate(view): deprecate output/confirmlink for consolidated output/url with 'confirm' option

Fixes #5810
Merge pull request #7442 from ewinslow/oo-config

chore(config): Move high-level elgg_*_config apis into OO service
Merge pull request #7438 from beck24/5810-url-confirm

deprecate(view): deprecate output/confirmlink for consolidated output/ur...
chore(config): Move low-level *_config DB API into OO service
chore(entities): Move entity sql logic into entityTable service
Merge pull request #7440 from ewinslow/oo-config-table

chore(config): Move low-level *_config DB API into OO service
Merge pull request #7447 from ewinslow/oo-entity-table

chore(entities): Move entity sql logic into entityTable service