Migrate Theme Options/Options Framework to Customizer controls

[rclations]

No description provided.

[benlk]

Past research on this topic:

• Database Update Scripts #1417 (comment)
• Add migration scripts for site blurb  #1423 (comment)

This will encompass:

• research how the Customizer prefers to deal with data
• losslessly morph the existing optionsframework metadata to theme mods format as part of Largo's upgrade function
• test for that upgrade
• provide shim function for of_get_option and of_set_option if possible for child themes to prevent immediately-upon-upgrade breakage
• recreate the Theme Options settings in the Customizer, possibly using "selective refresh" as described in Migrate Theme Options/Options Framework to Customizer controls #1438
• replace Largo's custom site icon logic with WordPress' in Migrate and Delete Custom Favicon Option #835
• check if Multi_Checkbox customizer control doesn't properly set initial values #243 is still an issue
• (low priority) fix largo_get_active_homepage_layout does not check whether the layout exists #1823

[MirandaEcho]

Options framework --> customizer