Added 'Edit marker frame' feature

[brunovalads]

Adde both the button and the strip menu option for editting a marker frame, using its Move method.

• [X] I have run any relevant test suites
• [X] I, the committer, have read the licensing terms for contributors (last updated 2022-07-15) and am compliant

[vadosnaprimer]

I suggest using an icon with just clock, since it looks too small otherwise.

[brunovalads]

Way better now.

[brunovalads]

@YoshiRulz

Is Clock.png your own work, or from some clipart library?

I editted an existing one: resized, hue-shifted, and manually pixel editted it. Is it ok, or I should make one from scratch?

[YoshiRulz]

It's fine to use whatever for now, I'd just like to know where it came from. It could save me from having to replace it later.

[brunovalads]

All requested changes done!

[vadosnaprimer]

Can't test myself due to build problems on win7, but what happens when you try to enter an invalid value?

[YoshiRulz]

Input should be validated by the new InputPrompt { TextInputType = Unsigned }.