Add support for more filtering when when adding a parent/child column to a table

[Nicklas Nordborg]

The functionality for adding a parent or child column to a table currently allow us to select a specific main type and a subtype of the parent/child item.

It could be useful to have more filtering capabilities. For example, in the list of patients we could then list child derived bioassays with subtype AlignedSequences and Pipline=DNA/Normal/WGS. The column would then only show us alignments from normal DNA samples and not from the tumor or RNAseq pipelines.

In theory it would be possible to use a very complex filter, but in practice we need to encode everything into the column definition string. This is currently /DIRECTION/ITEMTYPE/subtype-id/property. We need to add the extra filter information into this string without breaking existing definitions. Since the subtype-id part is always a numeric ID it would relatively easy to add more information to this field. For example: /DIRECTION/ITEMTYPE/subtype-id:filter-def/property

where we need make sure that filter-def is encoded in a way that doesn't break other parsing (eg. it can't contain '/').