Fix shortcut ambiguities

[shaavan]

Picks up #129 fixes #126

• This PR addresses and fixes the shortcut collisions.
• This PR takes reference from this commit.

Changes done in this PR:

Option whose shortcut is changed	From -> To	To avoid collision with
Size of database cache	D -> I	Display tab
Enable coin control	C -> a	Cancel option
Connect through SOCKS5 proxy	C -> S	Cancel option
Minimize to tray instead of taskbar	M -> T	Main tab

Also, this PR address this comment in #129, which was suggested to add with the original PR.

"Third party transaction URLs" string could be ended with :

[shaavan]

Updated from f77451c8c11b9d41f5b6fa8659d947b0c99051e7 -> dd536e97b19743898c531909731b7c40977e2cc9 (pr633.01 -> pr633.02, diff)

Changes:

• Added another commit that changes the shortcut for the Close option from l -> C without introducing shortcut collisions.

The reasoning for the change:

• Close action is marked with shortcut c everywhere else in the GUI.
• c is a more intuitive shortcut for Close action than l.
• There is no shortcut conflict introduced with this change.

[shaavan]

Updated from dd536e97b19743898c531909731b7c40977e2cc9 to cfe407c81d66ea4b14737208eb568dfd36265a73 (pr633.02 -> pr633.03, diff)

Addressed @jarolrod comment

• Changed Enable coin control features shortcut from i to a.

The reasoning for this change is explained here.

[shaavan]

Updated from cfe407c81d66ea4b14737208eb568dfd36265a73 to 5fde8fbe0850218403c54d0cee04ecb2f36d79a0 (pr633.03 -> pr633.04, diff)

Addressed @jarolrod comment

• Reverted to pr633.01. Corresponding changes include:
  • Changed Enable coin control features shortcut from a to i.
  • Changes shortcut of close option from C to l.
• Added a commit to addressing this comment in PR #129 from which this PR is picked.

Thank you very much, Jarol, for your thorough review!

[pablomartin4btc]

Since we are here, shouldn't we add a shortcut for the "Options" window under the "Settings" menu? Like Ctrl+O or Ctrl+Shift+O?

Another kind of unrelated comment but it's related somehow with one of the options ("Minimize on close" on Window tab) and the Ctrl+W shortcut. After playing a bit with some shortcuts and accidentally closing the app with Ctrl+W (Ctrl+Q is the shortcut to close the app specified on the File menu), I found this was worked out on 15768, shouldn't be this "Minimize on close" be ticked by default?

[hebasto]

Maybe start from catching QShortcut::activatedAmbiguously() signals? It would help to test this PR, and translated GUI and future changes as well.