*Properties(): Switch to vector<string> for control modes

Update mode iteration accordingly.

Suggested by: [at]joakim-hove
*Properties(): Rename control mode (enum) variable

Four characters (cmod) is less readable than "cmode".

Suggested by: [at] joakim-hove
Rename helper: matchingProperties() -> historyProperties()

This more clearly reflects its actual purpose.

Suggested by: [at] joakim-hove
historyProperties(): Add note on numerically zero defaults

This is a hint to a future maintainers that the subsequent control
modes are unconditionally supported.
historyProperties(): Extract BHP limit if not defaulted

This fixes a programming error introduced in the refactoring of
Schedule::handleWCONProducer() (commit 3889e92).  When there is a BHP
limit in WCONHIST, we obviously need the value specified in the input
deck.  The refactoring led to the limit being extracted only in the
prediction mode.

Pointy hat: [at] bska