Add ability to define more complicated Final Series via DrawFormat and UndecidedTeam

[goodtune]

Related to #62 we need a way to manage unusual final series in the backend admin.

For example:

ROUND
1: P3 vs P6 Qualifier 1
2: P4 vs P5 Qualifier 2
ROUND
3: P1 vs "Lower placed qualifier" Semi 1
4: P2 vs "Higher placed qualifier" Semi 2
ROUND
5: L3 vs L4 Bronze Medal
6: W3 vs W4 Gold Medal

The above is presently not possible to define as a DrawFormat - I will need to add something to the grammar to deal with the label style of undecided teams.