Do not send preedit when closing Maliit Keyboard

It's wrong to send preedit on reset/close, it's the framework's or input
context's responsibility to handle preedit correctly when focus is lost.
Maliit Keyboard: Remove QtGui dependency from AbstractTextEditor

QtGui dependency was only needed for QKeyEvents. We can push that
responsibility to derived classes, however.

RevBy: TrustMe
Maliit Keyboard: Move AbstractTextEditor into core lib

Without the dependency on QtGui, the AbstractTextEditor class can now be moved
where it logically belongs. Also got into Logic namespace and fixed copyright.

RevBy: TrustMe
Maliit Keyboard: Make auto repeat behaviour a plugin setting

It feels silly having to re-compile Maliit Keyboard just to test different auto
repeat values. As a plugin setting (auto_repeat_behaviour, tuple of integers
[delay, interval]) it can be controlled at run-time. As a side effect,
EditOptions is gone.

RevBy: TrustMe
Maliit Keyboard: Move signal/slot connection setup into AbstractTextEditor

Gets rid of extra setup.[h|cpp] files that lived in libmaliit-keyboard-view.
The connection setup is now part of the core lib.

RevBy: TrustMe
Maliit Keyboard: Fix shift behaviour

There was an extra shift state in the state machine when in fact there are only
3 states for shift behaviour: no shift, shift latched and caps locked.

The actual problem is that when we switch to shift view, we forget that the
shift key was pressed. Whenever that happens, we won't receive a
shiftReleased() signal. But that requires a bigger rewrite to be properly
fixed.

RevBy: TrustMe
Maliit Keyboard: Unbind AbstractWordEngine and AbstractTextEditor properties

AbstractWordEngine::enabled property was bound to
AbstractTextEditor::preeditEnabled property, which is wrong given that even
without an active word engine, we can do nifty things with preedit, for
instance control auto-caps. As a consequence, having no backend configured for
the word engine (say, hunspell or presage) does no longer define
DISABLE_PREEDIT.

RevBy: TrustMe
Maliit Keyboard: Enable auto-repeat for arrow keys and space.

RevBy: TrustMe