[fix] rename timeout, register before run to avoid premature counter init

when importing tagget, timeout was starting on __init__, now it always starts on run()
new name for timeout value and callback functions, to avoid confusion
[fix] repeated function (typo)
[add] code comments, function description
[add] optional file parameter on __init__
rename tag_getter clase to TagGetter
[add] TagGetter __doc__
[add] __doc__ for functions
[rm] unnecessary import of pygtk,pygst and gst.interfaces
[add] description of reason for each import