The DirectoryExpander.expand cut to pieces. Filelist generation and HDR
parsing is to be moved to thread (still TODO item). Callbacks to handle
expanding the wx.TreeCtrl for both are carved out.
Callback for the progress indicator is added.
Progress animation preparation added.
Issue #20 fixed. Issue #19 is not fixed yet.
Merged after playing with reset to get back the modifications of today.
+ the progress indicator images added to the repo.
Revert "Merged after playing with reset to get back the modifications of today. + the progress indicator images added to the repo."

This reverts commit b6c0180eb27cf50f6833967b638b976285405d62.
Progress indicator animation images added.
Progress animation image name glob corrected.
- Threaded execution of recursive commands prepared.
- HDRSeqGenCommand class added
- All executeGen commands off-loads the time consuming tasks to thread
- Expander interface extended with getPath method to enable
HDRConfigPanel to modify HDR sequence configuration update
- getPath method of DirectoryExpander, ImageSequenceExpander added
- TreeCtrlWithImages stores the iterator for recursive commands
- TreeCtrlFrame: onCommandUpdate call callback only if not None.
- Recursive commands are implemented (not tested)