Empty, white preset dropdowns are confusing, better default is needed

[Pēteris Krišjānis]

Empty preset dropdown menus (Instrument effect presets, effect settings presets, any other preset dialog) with no text are just confusing, at least for me, so I suggest two things to improve that:
1. Give it gray filling, so it shows that there is no preset selected here;
2. Or even better, in default setting, give it in lightly grey letters "Enter your preset name here...", and if there is written something, before closing, give question to save this settings as preset or just lose that name of preset.

[David Corrales (davidcorrales)]

Since we're on a string freeze, I'll do this for 1.0.
I particularly like the idea of the usual helper text "Enter a preset name here..."