V2 -> V2a, pool fix, consistent ordering

[bwlang]

• correct pool identification for primers , all odd -> nCoV-2019_1, all e…ven to nCoV-2019_2
• updates to VarSkip v2a to correctly match shipped primer mix
• consistent ordering of tsv primer list

[replikation]

• @bwlang is the official name "VarSkipV2a" instead of "VarSkipV2" ? just to avoid confusion for users.
  and thanks

[bwlang]

The official name is "VarSkip Short v2". The "a" suffix is there to avoid confusion with the old version of the file and make it easy for people to know that they they are using the correct file. I hope we won't need a "b".

[replikation]

okay ill merge and keep the current VarSkip2 name. thanks