fix(qt): remove stretchers from Overview page when it's not needed

[knst]

Issue being fixed or feature implemented

Overview page has strange stretching on sides, which make balance moving left-right when window is scalled.

What was done?

Removed stretches for Overview Page from the sides, it makes window a little more balanced. This PR lets to do backport of bitcoin-core/gui#176 which improves behavior further more be increasing size of "transaction list" part of window.

How Has This Been Tested?

See screenshot. Resized window with/without patch, in "Discreet mode" off and on. Both looks not perfect but better than before.

Breaking Changes

N/A

Checklist:

• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have added or updated relevant unit/integration/functional/e2e tests
• [ ] I have made corresponding changes to the documentation
• [x] I have assigned this pull request to a milestone

[knst]

@knst knst force-pushed the fix-qt-overview branch from dd8b1ed to b9a2ce7

due to feature_proxy.py failed without IPv6. rebased on the top of develop