Use old *_build folder in case of a new branch
Rename every occurence of prepare with analysis

If you are new to the code the name prepare for everything that is
related to the analysisview can be confusing. Renaming them will make
it easier to see what the classes are being used for
drag'n'drop tracks on analyzeview
starting queuesize is set correctly
add option to analyzse crate/playlist to submenu

this path also does some minor code refactoring
adress rryans comments
Fix error if .sconsign.branch is missing. In this case, the current
*_build folder is re-used.
fixed scoping of some re-used variables
create branch folder in cache even when .sconsign.brach does not exists
removed if that always evaluates to true
Merge pull request #34 from daschuer/virtualize

Use old *_build folder in case of a new branch
fix creation of cache folder if already exists.
merge with kain88de/analysis