Feature selection within moses

Implement more options for feature selection within moses (keeping the old ones as default), such as

1) focus: which data points to focus on when doing feature selection. Choices are:
- all, all data points are considered
- active, only active data points are considered
- incorrect, only the incorrectly classified data points are considered
- ai, only active and incorrectly classified data points are considered

2) seed, how to seed the feature selection algorithm
- none, no feature set are used to seed the algorithm
- add, no features set are used but the number of features to select is the target + the number of features in the exemplar
- init, features of the exemplar are used to seed feature selection
- xmplr, the output of the exemplar is used as feature to seed feature selection

Implement "breadth-first" expansion. This means that a single exemplar can spawn several demes, each deme with a different representation and based on different features.