perf(repeatParserService): track groups by name 
perf(repeatParserService): track groups by name 

Use "track by" to track groups of choices by their name instead of
the $$hashKey. This way, existing items don't have to be
re-rendered when the array of items changes.

Closes #1721, closes #1722
Jefiozie/ui-select,oncompass/ui-select,looker/ui-select,Servoy/ui-select,billypon/ui-select,granteagon/ui-select-temp,piebe/ui-select,Crunch-io/ui-select,Jefiozie/ui-select,piebe/ui-select,ivanvoznyakovsky/ui-select,billypon/ui-select,MartinDeHaan/ui-select-submitform,granteagon/ui-select-temp,Crunch-io/ui-select,prakashn27/ui-select,Servoy/ui-select,angular-ui/ui-select,Jefiozie/ui-select,billypon/ui-select,oncompass/ui-select,Jobularity/ui-select,oncompass/ui-select,Jobularity/ui-select,WorktileTech/ui-select,WorktileTech/ui-select,angular-ui/ui-select,piebe/ui-select,WorktileTech/ui-select,angular-ui/ui-select,MartinDeHaan/ui-select-submitform,granteagon/ui-select-temp,ivanvoznyakovsky/ui-select,ivanvoznyakovsky/ui-select,MartinDeHaan/ui-select-submitform,Jobularity/ui-select,prakashn27/ui-select,Crunch-io/ui-select,prakashn27/ui-select,looker/ui-select,looker/ui-select,Servoy/ui-select