Fixed normalizePath() to strip out single dot dirs

Now removing "/./" and trailing "/." from the paths when normalizing.

Backport of c06d8bb0071839480f9e458e58630ca0c205b9cb
Files app backend now normalizes paths before rendering templates

Before rendering breadcrumbs or the file list, the paths are now
normalized. This prevents the UI to show "." breadcrumbs in case the
path contains sections with "/./"

Fixes #5848

Backport of 008c3b80d6cca6a15299afe01f150f075813df8c
Added missing test with leading backslash
Merge pull request #5883 from owncloud/stable5-singledotdirs

Stable5 single dot dirs