Add advanced selection functionality

[isaisabel]

As a user, I want to be able to select techniques based on their data. For example:

• Select techniques which have any annotations whatsoever
• Select techniques which have comments, or techniques which have comments matching a regular expression
• Select techniques which have scores within a certain range, or above/below a certain value
• Select techniques which have a certain metadata key present, or which have a certain metadata key:value pair

Ideally an expression editor would be provided allowing users to construct selection rules with simple boolean operations, e.g (score > 25 AND score < 50) OR score > 100