Add a navigation button which skips all unread emails in the current folder and
jumps to the next unread folder to the next unread email.

Created an attachment (id=8367) [details]
New Button UI

The new button will be added in QuickFolders Premium to the right of the blue
Navigation buttons:
# Previous Email
# unread / all toggle (green circle)
# Next Unread Email
# Mark thread as read and goto next unread thread

The function will traverse all folders (in the order of the folder tree)
outside of the current folder, regardless whether there are any unread emails
left in it. 
Special folders Drafts, Trash, Junk, outbound Queue will be ignored.

If the end of the folder tree is reached without finding unread emails, the
search will wrap around and start from the top. 

If no other folders with unread emails is found, there will be a sliding
notification (host program / OS must support these)  showing a message

"No other unread folders found, continuing in X"

Where X == current folder name.

it will then progress to the next unread email as normal.

Created an attachment (id=8368) [details]
4.9 prerelease 89

Test version.

Created an attachment (id=8369) [details]
4.9 prerelease 99

completed some more locales (Polish, Spanish, Portuguese, Chinese, Dutch,
Swedish, Italian) and improved the button design.

Created an attachment (id=8397) [details]
4.9 prerelease 113

Fixed a bug in Shim.getNextUnreadFolder() that made this only work if there
were unread emails only after current folder and not before.

Created an attachment (id=8406) [details]
4.9 prerelease 136

Added proper toolbar Icons for current 52.6 and future versions (59,60) of
Thunderbird

Created an attachment (id=8407) [details]
4.9 prerelease 137

Fixed a regression in options dialog that caused "Bling my tabs" to load
incompletely

Implemented in Releasee 4.9.1 - 13/03/2018