Chapter 8 - Minor revisions/corrections

Also a typo correction in Chapter 14.
Merge remote-tracking branch 'upstream/gh-pages' into gh-pages

Conflicts:
	chapters/08-extensions.md
Merge pull request #338 from dcmaf/gh-pages

Chapter 8: Extensions - Some rewording and corrections
adding note about underscore methods
removing in-place editing line
fixes #340 - patch for thorax example
dropping mac/linux/win specifics for bb
updating line about yeoman
Switching order of chapters 7, 8 for #343
removing second image from Marionette walkthrough as part of #343
adding example of bbb output for #322 point 4
adding earlier description of Backbone.LayoutManager for #322 point 6
adding explanations of precompilation, concat, minification for #322 point 2
cleaning up related tools/projects for #322 point 7
rearranging chapters as suggested in #322. Note that existing issues will need to be updated to reflect this.
Redoing all screenshots for practical 1 as a part of #333 point 7
updating install instructions for bb for #336
revising chapter on bbb and backbone boilerplate, updating to latest as part of #336
Fixes #310 - drops unnecessary model test in jasmine chapter