Fix the Fast Greedy check/error in Community Detection

[imbanunes]

Check the vizCommTab branch (tackles tasks #55 #65 #66)

What was done:

• added the visualization component to the community detection tab (plus hardcoded explanations of key concepts)
• added next/prev navigation buttons to move between tabs
• added a check for the Fast Greedy algorithm (when networks have multiedges)

Note that the hardcoded part is quite extensive. I wasn't sure how detailed/concise it should be but here is a first attempt.