[#617] Install from source doc updates
Merge branch 'master' into 617-source-install-doc
[#617] Build solr index with -r
[#606] Fix no resource error to not me flash message
Pass current user
[#533] Change paster commands docs to follow paster's conventions

In paster's documentation, a required field is shown in UPPER_CASE, and
underscores are used as word separator.
Add a test
[#533] Update paster's documentation and rename its title
[#533] Remove documentation of paster rights and roles.

They don't exist anymore.
[#621] Move extras_validation into __before

This fixes an issue where creating a new resource would crash in
validation if there was a custom field (using convert_to/from_extras)
with a name that sorted after extras validation alphabetically. Fixes #621.
[#708] Fix render_markdown() helper function
[#708] Switch over to use markdown_extract() not misc.py
[#708] Fix tests
[#708] Get markdown_extract() to use RE_MD_HTML_TAGS
[#708] Minor refactor
[#727] Clean up imports in core
[#728] Add ckan.tracking_enabled to app_globals

The ckan.tracking_enabled ini file setting was being ignored, so page
view tracking wasn't working. Adding ckan.tracking_enabled to
app_globals makes the setting work again.

Fixes #728
[#729] Handle languages in URLs when updating page view tracking summary

Page view tracking was failing when a language was selected:

1. Put `ckan.tracking_enabled = true` in your ini file
2. Run CKAN, visit a page with a language e.g. `/en/dataset/annakarenina`
3. Run `paster tracking update`. If you look in your db, in the
   `tracking_summary` table there'll be a row with `package_id`
   `~~not~found~~`.
4. Run `paster tracking export tracking.csv`, the exported CSV file will
   say 0 views.

If you visit the page without the language in the URL e.g.
`/dataset/annakarenina` then run the export command again, the view does
get counted.

This commit fixes the SQL used by the `paster tracking update/export`
command to handle URLs with or without languages at the start.

Fixes #729
[#541] Add docs for page view tracking feature

Add documentation for the page view tracking feature. There are still
some details to document, including how to show number of page views on
the pages themselves (eg. dataset views next to datasets) and how to
show "popular" labels next to popular datasets. It's also possible to
get a list of the N most popular datasets, for example for the front
page, perhaps this should be documented too.
[#541] Add popularity-sorting screenshot

Should have been added in commit 3eeeef2 but I forgot.