Handling "Selection (mark/middle mouse button)" is too spammy

[Daniel Hahler]

Please provide a timeout like one second for the input coming from "Selection (mark/middle mouse button)" - you do not want to have entries for each step when shift-selecting some input.

I do not have a test-case, but that should be obvious:
1. activate "Selection (mark/middle mouse button)" in the preferences
2. shift-select ("press shift and cursor-key") some text.

EXPECTED RESULT: only the relevant text should be put into the history
ACTUAL RESULT: every step is added to the history, making it look like a pyramid.

[Jérémi Couillard (couillard45682)]

Please fix this, i LOVE Glipper, so much better than the other clipboard manager, but i need a correct handling of the selection!