Tweaked Maze Generation

* Changed the way in which sections are created. Previously, sections
would take in all the rooms within their range and then add as many
rooms as necessary to meet the minimum door capacity requirement. If
that was impossible, then the whole section would be discarded. That
extra step has been removed to prevent arbitrarily large sections.
* The capacity of a section is now estimated after removing all the
frontier rooms (those just outside the inclusion distance). Previously,
they would artificially reduce the estimate. Sections should meet the
minimum capacity more easily now.
* Changed the max distance value for choosing which rooms are part of a
section. The value was previously selected randomly and applied to all
sections. Now it's selected randomly for each section.
* Added a loop to MazeDesigner that repeats the design process if no
maze sections generate. This could happen if the designer is unable to
assemble any sections that meet the minimum door capacity. The chances
of that occurring are incredibly slim though - less than 1 in 10,000.
* Changed the formula for estimating the door capacity of a room. A
slightly larger area is required for each door now.