Install dependencies and change to system python in .travis.yml

- Install dependencies manually that are not on pypi
- Use system python to install packages so they can be imported in
  postgres python triggers
Increment collection's minor version when a module is republished

This includes:
 - add a row in the modules table with the new minor version
 - copying the collection tree with the modified documentids
Transform cnxml to html when a module file is added
Adds a baretext field to the module fulltext index table.
Storing the baretext, which is used by the index, enables us to provide highlighted snippets for search queries without doing the transform each query.
Provides schema functions and triggers for fulltext indexing.
Adds useful object representation code.
Adds a test for fulltext search and fulltext indexing test data.
Updates the travis-ci build commands to include plxslt.
Updates the readme with more detailed database install instructions.
Merge branch 'cnxml-to-html-v2' of github.com:karenc/cnx-archive into karenc-cnxml-to-html-v2
various import and SQL fixes
only trigger on index file
assorted fixes: speed, correctness, ball-of-wax
test changes to match trigger work
Use generated module_ident and insert index.cnxml last in tests
Modify .travis.yml to use cnx-upgrade cnxml-to-html-v3 branch
Renames the column to module fulltext column to fulltext. Fixes test data.
Assert the number of modules before and after republishing a module
extra logging for now
Fixes #55