Change mimetypes from textmate added languages to better known mimetypes

When I add a new language, the mimetype is just text/x-ext-a and the next one will be text/x-ext-b. But this is not really usefull, when I use the mimetype for some more specific stuff for example adding code completion items or adding actions to those mimetypes. I can't guess, when I have 10 new languages, which one is one.

Solution is, and most of the time it is using the extension.

So adding a new language for kt (Kotlin) files, it will be text/x-kt, for cs (C#) it will be text/x-cs for feature (cucumber feature files) it will be text/x-feature. This is way better IMHO. Using ext-a, ext-b, ext-c says nothing.