Check permissions unix-way

Check if path write flags are enabled for the current
user, group or everyone else.

The permission logic was failing during the "first time"
scenario, where the activity was opened for the first time,
because there was no data file to read from in the first
place.

This patch solves the logic and also does proper permission
checking.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Merge pull request #1 from tchx84/unix-permissions

Check permissions unix-way
cleaning up uitests
Merge branch 'master' of https://github.com/walterbender/training
v1.28
safe text handling
more robust UID generation
revamp USB checks
lots of changes to accommodate Paul's new content
more merging of Paul's content
finished merging Paul's changes to Journal; removing old content files
better handling of close alert
add test for network connection
news for v1.30
new content
tweaks to new content
removing old content
v1.31
add email addess to progress bar
fix typo in sync