* Update dep github.com/markbates/goth
* Update dep github.com/blevesearch/bleve
* Update dep golang.org/x/oauth2
* Fix github.com/blevesearch/bleve to c74e08f039e56cef576e4336382b2a2d12d9e026
* Update dep golang.org/x/oauth2
* add google+
* sort signin oauth2 providers based on the name so order is always the same
* update auth tip for google+
* add gitlab provider
* add bitbucket provider (and some go fmt)
* add twitter provider
* add facebook provider
* add dropbox provider
* add openid connect provider incl. new format of tips section in "Add New Source"
* lower the amount of disk storage for each session to prevent issues while building cross platform (and disk overflow)
* imports according to goimport and code style
* make it possible to set custom urls to gitlab and github provider (only these could have a different host)
* split up oauth2 into multiple files
* small typo in comment
* fix indention
* fix indentation
* fix new line before external import
* fix layout of signin part
* update "broken" dependency
