some code refactoring for better naming, reset option, remvoing unnecessary code ...

better naming for the settings option

specify the tag filter option 'NOT' as 'NOT OR' and 'NOT AND'

minor bug fix, add missing import io

implement 'not' option for tag filter and minor code enhancement

make tag filter mode ('and' / 'or') switchable

fix vertGroups in calculateVolume

uniform usage of sys.platform and minor bug fix

use list instead of dictionary for plugins to load

bug fix: update plugins list, after zipped plugin was installed successfully

set explicit bone weight warning to debug level

fix update problems in measure plugin

avoid double unit conversion

fix measurement plugin

add weight option to settings