front fixes:
 - duplicate adder button,
 - "add content" buttons in design mode
 - protecting styles from overwriting by template
add filter by parent_id for trees created by fx_data_content_page
put assets to the end of the <head> to be able to add something template-specific before running all other scripts
(in fact this is not a real solution, we need more control here)
1. throw exception for sql errors instead of dying
2. and wrap loading config from db with (fake) try-catch block to prevent fatal when the migration for fx_option table not ready yet
tiny cleanup