ui supports.
Add a new worker SelectElement to deal with element selection. A injection script too.
chapter page working.
Small improvement of displaying in the positions of the buttons of a modified page.
Add a python http server. And routine for XHR.
Server working.
cgi working well. And not serving the null url.
Ensure all image loaded before modify page worker next step.
Should remove tab. Not for test any more.
Logs for ModifyPage. Remove log for modifyInjectCode.js.
Fix the bug that will cause timer function fails to restart.
Merge branch 'chapter_supports'

* ImageServer.py: New file. A cgi python server to save mhtmls to
directories filled with images.
* controller.js (TabController): Refactor to cooperate with
ChapterController.
(ChapterController): Use to controll TabControllers to save manga pages.
* manifest.json: Add pageCapture permission.
* modifyInjectCode.js: Wait for image loaded and save the state. Further
wait for message to notify this completion state.
* popup.html: Add field chapter query string.
* popup.js: Handle chapter query string.
* selectorInjectCode.js: New file for select manga pages anchors.
* workers.js (InstallObserver): Only the first title as title.
(ModifyPage.modify): Start timers until the target tab has responded
with okay.
(SelectElement): New class. Use selectorInjectCode.js to select manga
pages urls.