Fix Problem with user component loading GiiModule

For a simple check if gii is installed it does not have to be instanciated. So gii will not overwrite existing application components. 

Related issues:
yiisoft/yii#1906
yupe/yupe#381
Merge pull request #478 from cebe/patch-1

Fix Problem with user component loading GiiModule
fix tableprefix
small fix default tableprefix is "yupe_"
small fixed #470 in modulesinstall
Merge branch 'master' of https://github.com/yupe/yupe.git