Introduce keyboard scroll flag in Virtual Console

[Pac72]

This is the second try to fix #1443, after a first attempt with pull request #1584 that covered only VCButtons. The approach on this change is completely different: introduce a flag to choose whether or not to use arrow and PgUp/PgDown keys to scroll Virtual Console. When the flag is disabled, all the keys are available as key combinations on the controls.

Side changes:

• in assignhotkey.ui the former QLineEdit has been replaced by a QLabel to allow capture of (almost) all the keys (the QLineEdit consumes at least backspace, delete, home, end, left and right cursor keys)
• the CTRL+key combinations are completely blocked

Closes #1443

[coveralls]

coverage: 32.056% (+0.02%) from 32.034% when pulling e0912e5a06d5b044bc1671c376b3441002206bf1 on Pac72:issue-1443-vc-settings into c1f5846de11931e43213afbd49b7cbac1031e23d on mcallegari:master.