Initialize TilesetView::mMarkAnimatedTiles as appropriate

The marking of animated tiles is expected to be enabled by default.  It
is disabled in the tileset view used to pick the animation frames in the
Tile Animation Editor.

Coverity-issue: 1165697 (Uninitialized scalar field)
Added missing initialization

This pointed could never be referenced, but it's better to initialize
it anyway to avoid future issues.

Coverity-issue: 1165696 (Uninitialized pointer field)
Removed the default Change constructor

It was never getting used, but it was needed for compilation. Changed
some code around so that this default constructor does not need to be
declared.

Coverity-issue: 1165695 (Uninitialized scalar field)
Fixed two uninitialized variables

Though I don't see how either could cause any issue, it's better to
initialize them anyway.

Coverity-issue: 1165694 (Uninitialized pointer field)
Initialize PythonPlugin::pTiledCls

Coverity-issue: 1165692 (Uninitialized pointer field)
Initialize MiniMap::mRedrawMapImage

Not that it could cause any problems when it was true by default, but a
redraw is not needed right after startup.

Coverity-issue: 1165689 (Uninitialized scalar field)
Initialize BucketFillTool::mLastRandomStatus

Coverity-issue: 1165681 (Uninitialized scalar field)
Fixed confusing return value in PythonPlugin::write

Warning from clang++:

  warning: implicit conversion of NULL constant to 'bool'
  [-Wnull-conversion]
Added a missing 'break' in CommandDataModel::setData

Though since there was an additional check on the column, the missing
break was not causing any issues.

At the same time I've made sure the EnabledColumn is no longer editable.
It should only be marked as checkable.

Coverity-issue: 1165677 (Missing break in switch)