ENH: unify use of dictionary method names

• previously introduced getOrDefault as a dictionary get method, now complete the transition and use it everywhere instead of lookupOrDefault. This avoids mixed usage of the two methods that are identical in behaviour, makes for shorter names, and promotes the distinction between "lookup" access (ie, return a token stream, locate and return an entry) and "get" access (ie, the above with conversion to concrete types such as scalar, label etc).