Make some methods non-inline, and add method descriptions.

Change-Id: Ib8d5fa666827a7f97035ad37d05e305bb920c300
bnc#822173: Initial work on exporting pivot cache and pivot table to xlsx.

Still not perfect, but it somewhat does work.

Change-Id: Ic248e20f7ab18a37f56b2034f57551dded956bab