chore(structs): Add collection interface and array-based implementation for use in core

Fixes #7409
chore(tagcloud): move site tagcloud functionality to the tagcloud plugin

fixes #7140
chore(tagcloud): moved tagcloud theme sandbox output to tagcloud plugin
chore(tagcloud): moved tagcloud related views to tagcloud plugin
chore(composer): Remove composer lock file

Locking dependencies could cause problems if dependencies were updated
on one platform to versions that are incompatible with an older but
still supported platform. (E.g. updated on PHP 5.6 but then tests run
and fail on PHP 5.4 because dependencies are no good).
chore(cache): Add some new caching APIs for internal use
chore(datalist): Convert Datalist to use new caching APIs
chore(js): Don't declare the same `var` more than once since they're hoisted
chore(js): Declare vars only once since they're hoisted
Merge pull request #7525 from ewinslow/js-upgrades

chore(js): Declare vars only once since they're hoisted
Merge pull request #7527 from ewinslow/js-friendspicker

chore(js): Don't declare the same `var` more than once since they're hoisted
chore(js): Clarify that the assignment in while loop check is intentional
Merge pull request #7529 from ewinslow/js-assignment-intentional

chore(js): Clarify that the assignment in while loop check is intentional
Merge pull request #7474 from ewinslow/cache-refresh

chore(cache): Add some nice new internal APIs for caching
chore(core): provide feedback when autoloader is missing

fixes #7220
feature(users): Username character blacklist can now be altered via plugin hook

Also removes hyphen from the blacklist making it a valid character by default.

Fixes #6189
Merge pull request #7512 from juho-jaakkola/username_blacklist

Username character blacklist can now be altered via plugin hook
Merge pull request #7515 from jdalsem/autoloader-feedback

chore(core): provide feedback when autoloader is missing
feature(webapp): Add support for a basic WebApp Manifest file

Fixes #7493
chore(metastrings): Move metastring table code into a class