added PluginEngine.load_plugins
moved move_file function to utils
(fix #7)(fix #5) GUI works, Requires and Scriplets order changed, some fields of Import' page validates.

GUI works and some other staff

Test folder removed

Some text changes

Final text changed

files names changed

Unneecessary files deleted

final changes before first pull request

Button on BuildPage now works fine

Space on end of file removed

Imports fixed
tags now support single or multiple values
- 4-tuple files changed to 3-tuple
- added single_value_tags list, assigning a list to a single value tag
  returns -1
- added mark_doc GUI helper
- comments changed to docstrings where necessary
- droped commented out statements
- changed object based arguments from None to proper data structure
  initalization
- used only 1 private field as requested
- argument out marked as required
- added method load_sources
- added dictionaries storing compression types, indexed by file-specific
  magic signatures