Make QuickFolders compatible with the current Thunderbird beta (67.0b2) in
order to prepare for the next ESR release in October 2019.

FOr back-porting, I created a new GitHub branch at 
https://github.com/RealRaven2000/quickFilters/tree/Tb-52

To Do: 
Use new preferences system. (See
https://developer.thunderbird.net/add-ons/upgrading-add-ons-for-tb68/list-of-changes-in-thunderbird-core#less-than-prefwindow-greater-than-less-than-prefpane-greater-than-less-than-preferences-greater-than-and-less-than-preference-greater-than)
Replace prefwindows with dialogs 
Replace groupbox elements with html fieldsets
Replace colorpicker elements with HTML input type color
Replace AddonManager (which is now a promise)

Github branch correction - for QuickFolders, this obviously needs to be:

https://github.com/RealRaven2000/QuickFolders/tree/Tb-52

Created an attachment (id=8621) [details]
4.15 prerelease 30

This version has been tested on Thunderbird 66.0b3 and 67.0b2 - there may be
some minor hang-ups in the options dialog not storing all values, please test
thoroughly. Especially any textboxes/pixel values should be scrutinized.

known issue: restoring tabs from the clipboard using the "Copy Tabs" feature on
"Advanced Options" tab doesn't work yet. Other than that, we're looking pretty
good. I tried my best to support lightweight themes in the "Bling my Tabs"
preview areas so you can get a good feel for what your color choices may look
like.

Created an attachment (id=8622) [details]
4.15 prerelease 56

Improved options dialog
added lightweight image preview in options
lightweight theming for current folder toolbar
Increased max version to Thunderbird 68

note: this version has no Asian locales (zh / ja / vi) due to an attachment
size limit on mozdev.org. All other locales will work.

To do: replace numerical textboxes with HTML elements

There is a way to make a hybrid Add-on that has both install.rdf and thus can
be accepted by Thunderbird 60 (or even older versions) and manifest.json for
the new web-extension format; I am planning to adopt this in the next version
4.15 for QuickFolders.

Created an attachment (id=8629) [details]
4.15.1 prerelease 38

The latest version of Tb daily 69 crashes because it doesn't like
document.createElement in a XUL document; so this version replaces the
functions with createXULElement for now.

More info:
https://docs.google.com/document/d/1rEPcu7ei-kK5Dvt7sBgqa_vP37QFIUtVd33JkCK1mvM/edit

Resolving Fixed with release 4.15.3 on 17/06/2019
this version is compatible with Thunderbird 68.0 beta 1 (the current version
for 68)