Feature updated core

• provide container methods such as front(), back(), push_back() etc that are commonly used in the STL containers. This should help with swapping code between OpenFOAM and other projects and (in the future) make the code easier to read for newcomers.
• reduce the use of SLList in a few more places to avoid repeated memory allocations within loops
• provide point/vector dist() and distSqr() methods for differences. This avoids intermediate variables and looping (should be more cache friendly).
• new mesh access method cellBb to return the boundBox of a mesh cell. Uses cached cellPoints (if available) or calculates from the face points. Eliminates similar code fragments that were scattered about the code
• improved functionality and efficiency for boundBox and treeBoundBox
• more consistent naming and handling of indexedOctree and treeData components.

Changes were originally rolled into MR !568 (merged), but grew too large for that.