Remove parameters for handle_load_build_url

Removed the parameters for the handle_load_build_url function. The way
that PyQt4 connects event handlers to widgets does not allow for passing
in parameters. Instead of using a parameter, the class-wide available
build_url_box widget is used to retrieve the build URL link. #21
Remove function calls used for testing from passives.py

Removed function calls from the bottom of the passives.py module. These
were only used for testing the backend code. This module will now be
tested through the GUI
Made a test setup for loading build URL

Made a test setup for loading and parsing a build URL through the load
build URL button.
Add code to passives.py to calculate passive bonuses

Added code to passive.py to calculate the actual passive bonuses with
their values for a given passive tree URL. Some nodes are currently not
parsed properly, but this is something that's being looked into.

Over the next week, all the skill nodes of the tree will be checked
(actually work in progress at the time of this commit), and testing will
be done with decoding of bitcodes.
Create unique dropdowns/level boxes for the support skills

Because how how PyQt4 event handling works, each dropdown menu for the
support skills and the levels needs to have a unique name. This way we
can identify which dropdown menu has changed, and in the future this can
be used to properly update the values displayed in the other dropdown
menus.
asdadsa
Fix bugs in support skill dropdown menus

Fixed a few bugs in the support skill dropdown menus. On initialization,
the dropdown menus are filled at first, and when all the dropdown menus
are filled, re-updated with the available values. Upon switching a
support skill, the other dropdown menus will have the list of values
updated.
Fix parsing of node descriptions

Worked on parsing of the node descriptions, so that there's a value
attached to the description, and the description is formatted in such a
way, that the value linked to that description can easily be placed in
the description for display in the statbox.
Display return value of the passives script in the statbox

Updated the GUI.py script to display the returned value of the passives
script in the statbox. What still needs to be done, is correct
formatting of the descriptions with values and grouping the descriptions
by type.
Update documentation in gui.py and passives.py

Updated documentation in gui.py and passives.py
Merge pull request #24 from PrutsendePrutser/feature-link-load-build-button-#21

Feature link load build button #21