Add Hook Customization to Customizer

[DangitRick]

This update allows users to add custom HTML to their site directly in the WordPress Customizer panel. Very powerful, very useful!

(Ideally, users should be able to add PHP code to their customizations too; the code is present in this pull request and works like a treat. However, it depends upon exec() which is prohibited by theme coding guidelines.)

[ineagu]

Hey @BrazenlyGeek this sounds cool and useful however from my point of view is more or less plugin space, there are a tons of plugins for custom html/php.

However just to let you know some news :)

• we acquired flat from the previous owner and since we do have our own process ( like different repo structure, not using bower/travis or grunt yet ) so for the moment we plan to keep both this repo and to create our own where we will continue the dev in our way ( not the best :D ).

I will try to keep an eye here too, also we are not used to contribution type of repo and I know is bad however for now we just wanna quickly change ownership and then figure it out :)

The new repo is : https://github.com/Codeinwp/FlatX and you can see has a more straightforward structure .