Re-check element names and modules to conform with Qt

[ChALkeR]

For example, 3fab595 («Rename TextArea to TextEdit to conform QtQuick») was not landed and needs to be redone.

There could be other elements that need renaming or moving.

Update: actually, I'm merging 3fab595 in #28, let's get that in for now.
I'm going to keep a TODO list here.

• Re-check TextArea and TextEdit.

  Atm, both of them are defined in TextArea, see 636b1e0 for details. Perhaps those should be split, perhaps TextEdit should at least have a separate file.

• Re-check Button — registerQmlType('Button', QMLButton); does not look valid.

• Re-check PropertyChanges — registerQmlType('PropertyChanges', QMLPropertyChanges) does not look valid.

• Re-check Component — registerQmlType('Component', QMLComponent); does not look valid.

• Re-check QMLDocument — registerQmlType('QMLDocument', QMLComponent) does not look valid.

[ChALkeR]

This should be done after merging.

[ChALkeR]

Everything mentioned here is resolved.