Render a warning when parsing non-static non-strings

[alexanderwallin]

The point of this extractor is to suck out static strings from your code and into a .pot file, so that you don't have to define a huge object of strings in a random file and then use key-value objects in the source code to render them.

I see two benefits with showing a warning when parsing non-static non-strings:

1. to remind of the above purpose; and
2. to give heads up on potential code smells when using mapped functions/components in a way they maybe weren't designed for.

This could be enabled or disabled using a config flag.