Add 7zip support to the thunderbird trunk builds

mail/installer/windows/7zip.bat

+cd 7zstage
+7z a -t7z ..\7z\app.7z *.* -m0=LZMA:d25m:fb128 -mx9
+cd ..\7z
+upx -9 7zSD.sfx
+copy /b 7zSD.sfx+app.tag+app.7z SetupGeneric.exe
+cd ..

mail/installer/windows/app.tag

+;!@Install@!UTF-8!
+Title="Mozilla Thunderbird"
+RunProgram="setup.exe"
+;!@InstallEnd@!
\ No newline at end of file

mail/installer/windows/installer.cfg

@@ -12,3 +12,4 @@ FileUninstallZIP          = UninstallThunderbird.zip
 FileInstallerNETRoot      = ThunderbirdNetSetup
 ComponentList             = xpcom,mail,talkback,deflenus,langenus,regus,offline
 LicenseFile               = mail/LICENSE.txt
+7ZipSFXModule             = other-licenses/7zstub/thunderbird/7zSD.sfx
\ No newline at end of file