add getSequenceAsString to Alignment closes #477
add getSequenceAsString to Alignment closes #477

Anaphory/beast2,Anaphory/beast2,Anaphory/beast2,CompEvol/beast2,tgvaughan/beast2,tgvaughan/beast2,tgvaughan/beast2,tgvaughan/beast2,CompEvol/beast2,Anaphory/beast2,CompEvol/beast2,CompEvol/beast2