Import: don't assume an empty file is a text file

Since in any case, the empty file has nothing to import and it's admitted by
SQLite as a valid database, it's better to revert to the previous behaviour,
where an empty file dropped or opened by the file manager was treated as a DB
and indeed worked.

The behaviour was changed by cfa4dee

See issue sqlitebrowser#2636

Simpler version for AppImage and branch name in the continuous release

The command `git rev-parse --abbrev-ref HEAD` is not returning the branch name
in the travis server, and for the version in AppImage filename it would be
enough to have the short commit id.

Note that these changes are branch dependant.

See issue sqlitebrowser#1092

Remover unused reference to the master branch

This command is failing

Update code according @mgrojo's review

Update Arabic translation (sqlitebrowser#2406)

sqlitebrowser#2405
# Conflicts:
#	src/translations/sqlb_ar_SA.ts

DB Browser for SQLite 3.12.0

Update version number for 3.12.0

Updating version number for 3.12.0-rc1

We're using 3.11.300 for the 3.12.0-rc1, in order to keep
numerically lower than 3.12.0, which will be used for the
actual release.

Only include the build date for nightly builds.

Our alpha and beta releases use patch numbers greater than 99, so
were being caught by the version string check.

Update version number to 3.11.2