Deleting unused images
Add link to OMERO Homebrew installation script to the doc page
Explain system-wide Python vs Homebrew Python installations

Note this commit does not make a final choice on a recommended strategy for
Python. The goal here is rather to present both alternatives and point at the
differences in the corresponding sections of the documentation page.
Expose the installation formula with Ice 3.4
Fix environment variables example block

- Remove deprecated BREW_DIR variable (since we are documenting the default /usr/local)
- Remove $ICE_HOME/python from DYLD_LIBRARY_PATH
Add links to the Homebrew and Python wiki page in Python section

Also add warning about `brew install` and virtual environments
Removing and updating images on policies.txt
Moving editor icon & fixing link
Fix incomplete sentence and multiple spaces reported by Blazej
merge dev_4_4 -D org -I include -E exclude: PR 368 (Cpp: Correct content and markup)
merge dev_4_4 -D org -I include -E exclude: PR 440 (Images tidy dev_4_4)
merge dev_4_4 -D org -I include -E exclude: PR 442 (Homebrew and Python)
merge dev_4_4 -D org -I include -E exclude: PR 443 (Policy images)