Fix known issues with Qt5 source package contents

The following known issues with source package contents need to be resolved:

1. The autotests should probably be omitted from the source packages (as was done for Qt 4). The autotests are mainly useful for people developing Qt itself (and will use the git repo's for that purpose), rather than for people developing applications with Qt. Omitting the tests will reduce the size of the compressed .tar.gz package by around 25Mb and the uncompressed package by around 190Mb.

2. Remove git-specific files such as .commit-template, .gitattributes, .gitignore and .gitmodules from the packages. The .gitignore and .gitattributes files can appear in subdirectories as well as the base directory of the package.

3. Remove the template license headers from the qtbase directory (qtbase/heeader.*).

4. Remove the qtbase/dist directory, except for the changes-<current-version> file, which should be moved to the base directory of the package.

5, qtbase/dist/README used to be moved to the base directory of the package, but there is already a README there now. Decide what to do with the content in qtbase/dist/README – is it still needed? Can it be merged into the new README or removed?

6. Decide whether source packages should include html documentation. Either way, the documentation sources probably don't need to be in the source packages as users are unlikely to build the docs for themselves.

7. Decide whether the syncqt script should be pre-emptively run when generating source packages so that users don't need to have perl installed unless they modify Qt headers.