Only calculate if necessary
Pass site size through heartbeat
Request the site size fvia heartbeat send
Check if constant is defined
Return true if transient exists

Previously it returned an array of the whole site files / folders - bad for performance
fix return type
JSHint config
Extract to a function
Fix a few linting issue
Regenerate minified
Account for new schedule
Remove unneeded code
Update Javascript
Adapt heartbeat pulse
No need to return the whole array
Pop in the directory sizes
Merge branch 'master' into issue-588

Conflicts:
	backupwordpress.php
Merge pull request #588 from humanmade/issue-588

Pop the site size in automatically once it's been calculated