[issue #9] proper bower-install/bower-dist

- The bower install task wrote the lastCheck time every time even if the
task actually failed. The reason is that grunt does NOT stop immediately
on fatal/warn as stated in doc but finishes the "surrounding" task. We
have to check manually if the install task went properly.
- The bower dist task did not copy minified versions of js and css files

These changes have to be pushed to the scaffolding project.
[issue #9] bootstrap resolution necessary