add wheat cultivars to the plants division
add wheat cultivars to the plants division

- New "wheat_cultivars" collection defined
- New "default" collection defined to exclude the wheat cultivars
(choosing triticum_aestivum as reference)
- New LastZ PWAs defined
- Plants protein tree is now computed over "default" collection
- New wheat cultivars protein tree defined

Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara