Significant updates to download page. Better flow, both for noobs and pros, with  links to PGP and SHA1 resources.

Conflicts:
	docs/start/download.md
Tweaked maven anything-url-search field. Removed dup "AND AND" bool modifier.
Source: {Maven|Sonatype} links to anything search, rather than dist search.
added html file extension for the release-notes
Added verify page for checksums and keys
Merge pull request #689 from grkvlt/0.5-download-page-simplification

Download page simplification