added file browser
[filebrowser] implement file browser
rewrite filebrowser based on fbrowser_ch
remove debug messages
handle http redirect
handle readonly library
improve code about getting local cache file path
[filebrowser] show error message when error happens
show error message when upload fails
handle encrypted library
open cache folder
remove the old version of a file when downloading the newer version
centralize the opened filebrowser and support multiple instances
Merge pull request #242 from Chilledheart/backport-1

centralize the opened filebrowser and support multiple instances
filebrowser now accepts dropped files
update assets used by filebrowser
Merge pull request #245 from Chilledheart/patch-10

update assets used by filebrowser
update assets used by filebrowser, replacing file_image this time
don't upload a directory
Merge pull request #246 from Chilledheart/patch-11

update assets used by filebrowser, replacing file_image this time