Revised tank model.

This is for #214.
Updated conversion script for revised tank model.

This is for #214.
Updated reference results.

This is for #214.
Merge branch 'master' into issue214_tankHex
Increased the tank height
Updated comment.

This is for #214
Updated reference results.

This is for #214.
Added figure.

This is for #214.
Added UsersGuide for storage tank.
Added UsersGuide for storage tank.
Merge branch 'master' into issue214_tankHex
Merge pull request #217 from lbl-srg/issue214_tankHex

Issue214 tank hex