Move custom filters as close as possible to modules that use them

As part of converting the Channel Manager to Angular the second step is to sanitize the current code base. For this we want to move custom filters as close as possible to modules that use them:

1. getByProperty → channel/sitemenu/tree
2. incrementProperty → internal function of SiteMenu service
3. startWithSlash → left side-panel
4. searchFilter → search component

The complete plan can be found here: https://docs.google.com/document/d/1RoGCnJSBXrvP0kdd0jGLzWNd6Cbv1ucCpbo0YLNUN5c