Add Handlebars.php to the project via composer
Remove ".idea" folder
Use sanitization for locale constants
Do not use HTML entities in "form.field.groupparent.root" local const
Fix AbstractStyle class path (see Issue #19)
Use Handlebars.php as template engine
Move client side templates into pages style
Fix tests for JS Mibew API
Add custom elements in the header after default ones

Move "header" block in the "default" pages style to the bottom of
header tag.
Merge remote-tracking branch 'upstream/master'