webgallery prototype from github/will-moore/webgallery

This prototype app has been started as a standalone web app repo.
Following discussion with UX group, we want to allow more widespread testing
and review of this code.
In future we will likely want to ship /webgallery as part of the main OMERO repo.
Adding webgallery to INSTALLED_APPS
Adding 'Gallery' link to TOP_LINKS in omeroweb/settings.py
Fix missing "-" in permission string.
Replace assertTrue by assertEquals
Fix test. Delete should happen at the end of the test.
Change date in header.
Load settings per user. Fix test
Trivial typos not affecting behavior.
Clean up some Python use of deprecated raise "string"
remove unnecessary Python imports of exceptions
Fix zip creation.
rebase of jburel's d2b7c42
Fix missing negation in ExportActivity.

This wouldn't cause any problems as the higher-layer logic
already appends the .ome.tiff extension to the file name.
Update submodules
Merge pull request #1104 from snoopycrimecop/merge/dev_4_4/submodules

Update dev_4_4 submodules
Merge pull request #1091 from bpindelski/exportactivity-fix

Fix missing negation in ExportActivity.
Initial {% comment %} fix to original_metadata in metadata_acquisition.
download_orig_metadata(imageId) No 'file' refs
Add back 'download' button for images / wells.
Fix ZIP file path creation code (see #10804)