libcore|Range: Making a range with a start point and size
Refactor|libappfw: Use TextDrawable in LogWidget

Instead of custom code for wrapping text and preparing text for
GL drawing, LogWidget now uses TextDrawable. Only the potentially
visible lines are allocated on the atlas.

Todo: Fix rewrapping, optimize and clean up.
Fixed|libappfw: LogWidget's rewrapping behavior after refactoring

Every call to TextDrawable::update() potentially changes the visible
contents of the drawable, so its return value always should be
acted upon.
Fixed|libappfw|GLTextComposer: Showing a portion of tabbed content

The visible line range was not taken properly into account when
laying out tabbed content for drawing. Also, when lines outside the
range are released, their metadata is still kept intact even though
the rasterized version is released from the atlas. This allows the
text layout to still be calculated.
Refactor|libappfw|LogWidget: Updating a cached entry

Entries are updated on the fly.
libappfw|FoldPanelWidget: Removed frame around fold indicator

Looks cleaner this way and is not confused with a button.
Fixed|libappfw|LogWidget: Layout glitch when new entries first appear
Refactor|libappfw|LogWidget: Fixed pruning, overall cleanup
libcore|TaskPool: Ensure pool is not deleted when the last task finishes

In taskFinished(), between remove() and isEmpty() the mutex guarding
'd' was released. This would allow ~TaskPool to finish before the
'd' is accessed again in taskFinished().
libappfw|LogWidget: Start rewrap from visible range

Also updated comments in the source file.
Merge branch 'ui-log-textdrawable'