implements the Householder transformation for quaternion matrices.

Translation of matlab code in arXiv:1203.6151v4. Not used yet.
improvements
improvements..
KnowlesHandy form_sigma now uses the Matrix class
fixing the code that was broken by 6af07d51eff180a379ac73aa568b1327f0f74039
Revert "fixing the code that was broken by 6af07d51eff180a379ac73aa568b1327f0f74039"

This reverts commit 03595b2e92c9da01ae21f3fde62fbdde70acd23d.
Revert "KnowlesHandy form_sigma now uses the Matrix class"

This reverts commit 6af07d51eff180a379ac73aa568b1327f0f74039.
Merge branch 'master' into btas-tmp