EDMS v0.2: Added some search.

This should make things easier to track down problems around a set of devices/parameters.

- Added some search options in the /last-reports page: It looks like this /last-reports?type=hello_from_python&type=hello_from_c&hostname="RA-1"&hostname="RA-2"
  - All fields must be matched (AND condition) and if there are more than one they must be all respected (OR condition)
  - All the fields must be searched using the JSON format (that's why we have quote)
  This closes issue #1.

- Changed the DB model to simplify joins between reports and properties

- Some code refactoring

- Event reports without a type are stored and the default type is "_" (it is kept for compatibility reason)

- The /last-reports links have changed, they now behave like search options