Brazilian portuguese translation

Fix for window being placed badly on the screen when returning to board mode from desktop mode on some environments

Caused problems e.g with podcast mode, where if the control and display
views were swapped in the preferences, the wrong screen would be recorded
when switching to desktop mode during recording of the podcast.
This happened even if only one screen was plugged in, so a black screen
was recorded in that case (at least on OS X 10.10)

(when an opque stroke was in the vicinity of a translucent one, it
became translucent itself)

    - Qt plugins and libraries (and associated files) bundled only if necessary
    - Dependencies corrected (for Ubuntu 14.04 and 16.04, at least),
    mostly manually for now
    - run.sh sets Qt plugin path environment variable (=> qt.conf
    no longer needed; removed)

Just commented out the line since I'm not 100% sure it can be removed
(though I can't find a case where it is useful)

- Separated building and packaging
- OpenBoard is now installed in /opt/openboard instead of
/usr/local/OpenBoard-$VERSION/
- Placed a shortcut to run.sh in /usr/bin (so it can be executed with
the `openboard` command)
- Corrected .deb control files to avoid warnings e.g when installing via
software center on Ubuntu
- Added xdg bindings so that .ubz files are recognized and opened
automatically with OpenBoard

- Moved the release scripts into their own folder to clean up the
repository root a bit

(Merge branch 'new-release-script-linux' into dev)

- "Importer" folder renamed "importer"
- corrected detecting of 64bit architecture
- build context file is created in build.sh