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.
Fix path to the logo in layout.handlebars
comments added
Merge remote-tracking branch 'upstream/master'
Rename "L10n" handlebars.js helper to "l10n"
Remove unneeded $page variable from PageStyle::render
Rename "header" block to "head" in operator pages' templates
Pass style name to operator pages' templates
Rename "layout" template to "_layout"
Use handlebars.php for dialogs' templates
Reorganize dialog style

Move client side templates from "handlebars_templates" to
"templates_src/client_side"
Fix undefined "mibewroot" var (see issue #21)