[WIP] Final BC breaks (I hope)

Renames:

- All references to **selectorName** replaced with **alias**
- All references to **propertyName** replaced with **field**

- Renamed **fieldExists** to **fieldIsset**
- Renamed **ascending,descending** to **asc,desc**

Notes:

- Iam not 100% sure if "field" is better than "fieldName". But it seems OK. Opinions?
- Do we infact need **fieldIsset**? Is it different from `$qb->where()->eq()->field('a.foo')->literal(null)` ?