ZeroVector creation fixes
implement BlockDiagonalMatrix class
copy row/column for BlockDiagonalMatrix
make QuadtreeMatrix extend ABlockMatrix
Generic abstract methods for ASingleBandMatrix
specialised overrides for ASingleBandMatrix
make ABandedMatrix implement ISparse
implement Matrix11
unsafeSet and unsafeGet for Matrix11
misc edits
misc Matrix11 overrides
misc Matrix11 edits
misc small matrix overrides
make Matrix11 final