testing.txt: Clean up text.
testing.txt: Fix subsubsection delimiters.
testing.txt: Add instructions about ICE_CONFIG.
testing.txt: Correct style and add Sphinx keyword.
testing.txt: Correct syntax and spelling.
testing.txt: Use inline Sphinx syntax.
testing.txt: Oxfordise the list syntax.
testing.txt: Change order of text, update syntax.
testing.txt: Clarify text meaning.
Merge pull request #462 from mtbc/rebased/develop/ci-titles

Adjusted titles of continuous integration developer pages (rebased onto develop)
merge develop -D org -I include -E exclude: PR 450 (omero: Python 2.6 is the minimum supported version)
merge develop -D org -I include -E exclude: PR 471 (Clean up testing.txt (rebased onto develop))