Enable Largo-style custom sidebars on "region" taxonomy term edit pages

[benlk]

See what's mentioned here: http://support.inn.org/article/62-categories

Related to #8.

[benlk]

https://github.com/INN/largo/blob/v0.5.5.4/inc/term-sidebars.php#L19-L23

[benlk]

Enabling that filter is not enough; the output of largo_get_custom_sidebar() is returning sidebar-single no matter what is fetched.

[benlk]

I don't understand why it was doing that. There was no reason in the code for it to be doing so:

• Term Meta post was correctly updated with that piece of term meta
• Saving the setting in the term edit screen correctly saved it (wow that code in Largo needs to be safed: https://github.com/INN/largo/issues/1481)
• the available sidebars reflected the ones that were saved in the Theme Options custom sidebars page

Somehow largo_get_custom_sidebar() was falling back and returning sidebar-single, when the function doesn't have code to do that. Putting widgets in the sidebars fixed that.

[benlk]

Closed with #36