Updated Latvian translation
help: url option added to continuous instructions

Explain that Boxes will download and install the continuous image
now that it's working.

https://bugzilla.gnome.org/show_bug.cgi?id=737113
unattended-file: Handle 'floppy' injection method

This script injection method was forgotten when we added handling of
injection methods and it broke express installation for windows.
unattended-file: Make injection_method, public

Use make use of this in the following patch from UnattendedInstaller.
unattended-installer: Remove a hard-coded rule

Instead of checking if distro of OS is "win", lets instead check which
installation method we are using.
downloader: Handle downloads of unknown size

Currently if size of file being downloaded is unknown, we download the
bytes but just ignore the bytes. This patch fixes this case by writing
the downloaded bytes to the file but just not reporting progress if size
is unknown.
downloader: Add a logger to libsoup session

If Boxes is launched with SOUP_DEBUG environment variable set, attach a
logger to libsoup session.
topbar: Remove now redundant work around
Added Arabic translation
Add Arabic to LINGUAS
downloader: Correct documentation comment

https://bugzilla.gnome.org/show_bug.cgi?id=738168
downloader: Move downloading to download class

The Downloader got rather complex lately. It is time that the Download
object takes the part of downloading things while the Downloader only
manages several downloads.

This widely extends the (now abstract) Download object so that it
handles construction of temporary files and the await_download
functionality. The actual download is done by the subclasses.

This approach allows extending this download system later with other
download methods (e.g. samba file shares among others) without changing
anything outside the download.vala file.

https://bugzilla.gnome.org/show_bug.cgi?id=738168