Index features by name instead of number

[andreaswolf]

The array of features is currently indexed numerically, while it would actually make more sense IMHO to have it indexed by name. This way, accessing a certain feature would be way faster and it is also guaranteed that a name can only be defined once. Additionally, the feature configuration from a package could be easily extended in a per-distribution Features.yaml file.

[mneuhaus]

i guess this makes sense here, i used the indexed array because i almost duplicated the implementation of the ViewConfigurationManager which uses a weight system to merge those in proper order. But since we're not merging here i think it makes sense to name them :)