SYM: Workaround a bug when VKB covers text input

Closes #32 - Text input is covered by VKB in landscape mode.
SYM: Disable header when VKB is active
SYM: Fix an issue when VKB state wasn't preserved

When having VKB open, switching to another application and returning to
TAO translator, VKB was hidden while it should remain in the open state.
SYM: Workaround a problem with VKB

When having VKB open, switching to application with VKB open and
returning back, `inputContext.visible` is set to false while VKB is
still visible. This seems to be a bug in Qt or even lower.

The workaround assumes that when Symbian reports that application window
is partially visible and text input area is focused, then this is VKB
that partially covers the window.
SYM: Don't allow interaction with underlying components...

...when text input is popped out. Also, made some slight layout
adjustments.
BB10: Better support for dark theme

Dark theme is default on devices with OLED display and some resources
where not visible due to being dark too.
BB10: A small fix for BlackBerry 10.3

In BlackBerry 10.3 title in white theme is not branded anymore so title
text is badly visible (white text on light background).
Allow swap when source language is set to autodetect

When source language is set to autodetect and there is a detected
language, allow swap and do it with detected language.
Fix `const Language` -> `const Language &` in canSwapLanguages()
Google,MST: Don't allow to swap same languages

E.g., English with English.
BB10: TAO Translator in share targets for selected text

It's now possible to select a text in any app, press "Share" icon and
select TAO Translator from the list of targets. The text will then be
translated in TAO Translator.
BB10: "Share translation" button