gnucash-htdocs master: Add link to flathub

[Frank H.Ellenberger]

Updated	 via  https://github.com/Gnucash/gnucash-htdocs/commit/ef2735a8 (commit)
	from  https://github.com/Gnucash/gnucash-htdocs/commit/bfee1336 (commit)



commit ef2735a8e698d3da24b42be94fe66d08f3109df4
Author: Frank H. Ellenberger <frank.h.ellenberger at gmail.com>
Date:   Tue Sep 10 06:20:12 2019 +0200

    Add link to flathub



Summary of changes:
 download.phtml              |    9 +-
 externals/global_params.php |    1 +
 images/icons/flatpak.png    | 1144 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 1153 insertions(+), 1 deletion(-)
 create mode 100644 images/icons/flatpak.png