Run session creation in system context

In an effort to get rid of the periodic failing
tests with:
```
java.lang.IllegalArgumentException: No valid permissions available!
DUMMY permissions are not intended for copying. Make sure that you have
not passed omero.group=-1 for a save without context
```
make all calls to `SessionManagerImpl.createSession` run with an
explicit context for the system group.
Update dates in copyright headers.
Fix help message in download.py.
Handle ResourceError in download.py.
Fixing CSS for Javadocs
Rework the menu spacing
Combined style for v1.6 and v1.7 of javadocs
Encode HTML in tag name
Merge pull request #2441 from jburel/rebased/develop/log-file-truncated

Log file truncated (rebased onto develop)
Merge pull request #2440 from jburel/rebased/develop/scrollable-menu

Scroll menus. (rebased onto develop)
Merge pull request #2447 from rleigh-dundee/cpp-modularise1

OmeroCpp: Split ObjectFactoryRegistrar and remove unneeded includes
build: Remove support for Ice 3.3
Remove obsolete, broken and unused scripts
merge develop -D org: PR 2127 (Working view to email announcements to selected users, groups, email addresses and/or all users)
merge develop -D org: PR 2256 (Tablet drag handling)
merge develop -D org: PR 2258 (Truncate js tree dynamically 12161)
merge develop -D org: PR 2269 (ROI improvements)
merge develop -D org: PR 2336 (New tagging dialog)
merge develop -D org: PR 2357 (Generate Python API reference with Sphinx)
merge develop -D org: PR 2362 (Remove .jy from script names)