[GNC] Build on 18.04

[Colin Law]

Following the instructions for building GC 3.x on the wiki [1] has
been accomplished on Ubuntu 18.04 with little difficulty, so many
thanks to the contributors to the wiki.

Just one small issue so far, the icons to the left of the account
names are all showing as a little no entry sign, which I guess means
the icon is missing.  Does that mean I have missed something or is
something missing from the build?

Colin


[1] https://wiki.gnucash.org/wiki/BuildUbuntu16.04