reorganize Readme

Moved paragraphs around so least technical (most user-oriented) is on top, then tech/contributing (hacker info) is near the end.  This allowed to streamline the prose, but I tried to avoid changing the text as much as possible.

Linked blog in welcome section (great for finding features; helps users decide if Brackets is for them).

Used H4 vs **bold** for sub-headers.
more terse, less repeated text

(note to self; don't Push with only 4 hours of sleep)
more terse, less repeated text, ordered helping steps
reorganize getting help
Use Python syntax highlighting for .wsgi file extensions, ie. Python web apps using mod_wsgi.
Sort issues fixed on the Working Set and Project Tree
Added transition to Quick View Extension.
Revert unneeded changes to jsTreeTheme
Using variables for warning colors.
Merge branch 'master' of https://github.com/adobe/brackets into larz/issue-4392
Remove default extension from untitled documents and new files
Fixed Quick View animation:
* Simplified positioning calculations so we don't need to keep constants in sync between the CSS and the positioning code
* Changed from using `offset()` to `css()` to set left and top (`offset()` wasn't working with the non-default transform point)
* Made the animation slightly faster (and tweaked inline editors to match)
* Made the animation grow from the top when the bubble pointer is attached at the top
Merge with Master and fix Conflict Issue
Replace the title's {0} with 'File' or 'Directory' in the illegal characters message
Fixes after review
Fix quick view unit test to not rely on offset() for popover
Type fixed on the return description
Add unprefixed versions of animation properties
Merge pull request #4491 from TomMalbran/tom/issue-4453

Issue #4453: Parameter "{0}" appears in the invalid filename title.
Merge pull request #4485 from adobe/nj/animate-quick-view

Animate quick view popup