set proper keyboard shortcuts for Save and Save As actions

[Mystael]

As it was mentioned in this issue, keyboard shortcuts for save and save as actions do not behave like in most of other applications, because they listen to the CapsLock.

After this change it doesn't matter anymore if the CapsLock is turned on or off, as the save as action is invoked by pressing Ctrl+Shift+s or Ctrl+Shift+S keys combination.

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[Mystael]

@googlebot I signed it!

[zainafzal08]

Very elegant fix! Thanks for the PR :D We'll try to bundle this in with the next release of the text app (sadly it might take a couple weeks to get to you).

[BugsNash]

Fixes #523