Changed skillPrereqEditor prereqType to use a computed observable
CoffeeScript style improvements

Removed unnecessary parentheses from function calls.
skillPrereqEditor: clickSelectTarget improvement

clickSelectTarget now checks if any changes are actually needed.
Fixed memory leak in skillPrerequirementEditor.js.coffee
Added placeholder text to search box in skillPrereqEditor
Fixex a bug in skillPrerequirementEditor

Removal and addition of prerequirement skills were not updated
correctly in the results list.
Changed skillPrereqEditor results listing

The results list now shows all current prerequirements when there
are no search terms and when there are search terms, only search
results are shown.
Increased skillPrereqEditor search box width