Enable Sorting in Matrix

[alexsb]

We've decided to go for full fledged sorting in the matrix.

We want to add a sorting item to all columns, like this:

(this is font awesome I think)

Active sorting is color-highlighted. Otherwise, it's light-gray.

We want to sort the following things:

• [x] All numerical and categorical columns (as already implemented)
• [x] Sorting by Clusters (add button to the top left corner where there is whitespace. Label: "Sort by Clusters".
• [x] Sorting alphabetically (add button to the top left corner. Label "Sort Alphabetically"
• [x] Sort by edge weight. We will take the sum of both edge types to sort by, in case of multi-typed edges.

[dwootton]

• No need for the histogram, just the sorted icon with the color change, right?
• Additionally, should I implement descending sorting?

[alexsb]

Correct, no histogram. No, only sorting from large to small.