Superinfection needs unit testing

[ArtPoon]

These can go into test_simDyanmics.R, test_simOuterTree.R and test_simInnerTree.R

[ArtPoon]

@WongDWai - please submit a PR from your branch when unit tests are done

[ArtPoon]

Closed with #172

[ArtPoon]

• This test script should not contain its own .filter.firsts and .relabel.nodes function definitions. Otherwise there is no point to having the unit tests (the copies within the script may be fixed but those in the actual code base would remain broken). I have removed these from the script.
• It is not necessary to call library(ape) within the test script, etc.
• .get_outer_with_superinfection should be run once only by the developer and then the seed that generates the desired output should be hard coded, or the results added as test fixtures.

[ArtPoon]

I have addressed the first two points in the main branch, please fix the third @WongDWai