Use Homebrew Python rather than virtualenv

With recent changes brought to the main Homebrew repository, virtualenv Python
cannot be used by the Formula installer. To reduce maintenance burden, this
commit now installs Homebrew Python instead of a virtual environment. All
Python dependencies should be installed there during testing.
Fix scc installation
Create virtualenvironment (using Homebrew Python) for OMERO dependencies

- Use pip install virtualenv to install a virtual environment
- Activate the virtual environment only prior to running omero_python_deps
Install Genshi using brewed Python
Merge pull request #1278 from joshmoore/insight-connectors

Remove synchronization from insight connectors/gateway
Merge pull request #1291 from joshmoore/10970-script-replace

Pass context to script helper (Fix #10970)
Merge pull request #1293 from jburel/close-import

Close import
Merge pull request #1294 from aleksandra-tarkowska/11120_dropdown_menu

making Group/User dropdown menu configurable, close #11120
Merge pull request #1297 from jburel/cancel-all

Cancel all
Merge pull request #1299 from joshmoore/11017-instrument

Handle trans. range before filter (Fix #11017)
Merge pull request #1290 from mtbc/fslite

change config property name away from fslite
merge develop -D org -I include -E exclude: PR 991 (Add support for Ice 3.5 (develop))
merge develop -D org -I include -E exclude: PR 1132 (Repository API)
merge develop -D org -I include -E exclude: PR 1251 (Improve the logging during image import (see #11020))
merge develop -D org -I include -E exclude: PR 1269 (Update develop submodules)
merge develop -D org -I include -E exclude: PR 1270 (Show chgrp target tree if Projects OR Datasets exist. See #10917)
merge develop -D org -I include -E exclude: PR 1287 (Matlab examples fix (rebased onto develop))
merge develop -D org -I include -E exclude: PR 1288 (11109 chgrp fails on links)
merge develop -D org -I include -E exclude: PR 1292 (Do not flush all thumbnails when refreshing.)
merge develop -D org -I include -E exclude: PR 1300 (Channel edit)