do not load Bootstrap in non-admin controller for non-bundle themes.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| Refs tickets  | #2041
| License       | MIT
| Doc PR        | -

of course I am :smile: I'm just not seeing how this would break BC. Since it seems unlikely to be used outside of the core. (I found a second keyboard with a working "H" :tada: )