File: Symbolview does now append new items (sent by the FileMonitor) without reloading, first step to faster rendering of large filelists ...

Filesystem watch: watched directories now filters hidden files correctly (refs #1955) and transmits small changes within the event
- for upto 10 file changes detailed informations are provided (get_file_list style) - for none existing/accessable files only the name will be transmitted (and root/ext); key: subject_infos
- for upto 25 file changes only the list filenames will be transmitted (including the names of delete/moved files); key: subject_names
- for any amount of file changes the total affected file count will be transmitted; key: subject_count
- the path of the directory is provided to reconstruckt the fill path of any given file; key: path
- also removed broken and unused recursive get_file_list (via deep=True argument)

File: sorting in different browser, fix #2032, fix #2000. Several updates to our coding conventions, removing unneeded variables

- complete revision 1827

File: Make icon size selectable for the FileSelector, which fixes overlapping of icons and names for tiny view in selector

        - extend error message if a file cannot be read

filebrowser: removed permission-effects on drag and drop (too slow), fixed chrome bug on drag and drop

- check permissions when drag and drop
- hide edit tools on touch devices

(transplanted from ad6797117b84145d9671b48b670ba05fd52fbbb0)