Theme-Sniff-Issue-Format

[New sniff] No disabling of the admin toolbar
#### Rule:
**ERROR** : No hiding of the admin bar - check if `show_admin_bar( false )` is called or if `add_filter( 'show_admin_bar', '__return_false' )` is somewhere in the code. 

Ref: https://make.wordpress.org/themes/handbook/review/required/#core-functionality-and-features

#### Theme check file covering this rule:
https://github.com/Otto42/theme-check/blob/master/checks/adminbar.php

#### To do:
- [ ] Create unit tests
- [ ] Create new sniff