Access2Base - New TempVars collection and TempVar objects

TempVar objects contain variables (name/value pair) that can be dynamically created
and removed by macros.
They're useful to transmit values from one document to another, e.g. an .odb document and one or more non-Base documents.

Change-Id: I2cb5b3e27620eda16bdeaf59788b80c393fe7d9c