Update from transifex

Fix one instance of broken xml in a translation
Fix up shell update description

When checking for update through the system menu, they will automatically
begin to download and install when found.
[endlessm/eos-shell#4347]
Use consistent markup for Enter key

The <key> markup is the correct annotation
[endlessm/eos-shell#4346]
Remove the article about airplane mode

It has been removed from our system
[endlessm/eos-shell#4351]
Remove reference to writer printing icon

We don't have that asset, so well cut the text that references it
for now.

[endlessm/eos-shell#4237]
Merge pull request #17 from endlessm/shell/4237

Remove reference to writer printing icon
Merge pull request #16 from endlessm/shell/4351

Remove the article about airplane mode
Merge pull request #15 from endlessm/shell/4346

Use consistent markup for Enter key
Merge pull request #14 from endlessm/shell/4347

Fix up shell update description
Update pot file
Update from transifex