5.0 prerelease 100

Latest prerelease, some minor changes

• added a proper update / installation landing screen that can be fully localized
• all links to our support site / web shop are now using secure protocol (https)
• consolidated icons - thanks to @Paenglab for his fantastic work
• removed obsolete code overlaying filter list (which may have had side effect in my quickFilters Add-on)

Please report any bugs at issue #8

To install, download the xpi file below to hard drive and then pull the file into Thunderbird 78 Add-ons Manager.