!Wait with code reviews for this one. A. Monti working on the code!

In the VSE it isn't easy to see what strip is the active one and what is the rest of the selection, this is caused by a combination of the strip texts written with too much contrast, strips going darker and handles lighter during selection, and too thin and opaque outlines. Also the triangle handles looks dated and not industry standard. At some point, the strip image thumbnail patch(cover strip with images) will be finished and showing strip selection by changing strip color will not work anymore, so outlines will be needed, and for the same reason large trim handles will not work either.

This patch removes all the strip/text color changes when selecting, and adds wider outlines in a palette of colors in consistency with selection in the 3D View - white, yellow and orange and it lightens the strip texts from pitch black(nothing else in the UI is this color), into soft greys, in order to make the texts less attention craving, since we want to focus the attention on what is selected.

After/Before:

In order to keep this patch simple, an additional patch for subtle rounded corners on strips and handles as a line to follow the subtle rounded outlines is being discussed in the VSE chat, maybe @Alessio Monti di Sopra (a.monti) will take a look at that. Also theming of the selection colors should be in a patch of its own. Or in other words this patch do not aim at solving all challenges of the strip drawing, but just a first step of improvements.