Freeze exception request for Lubuntu install slideshow

[Dylan McCall]

Sorry about the extra messages! This one is a smaller freeze exception
request for the Lubuntu install slideshow.

https://bugs.launchpad.net/ubuntu/+source/ubiquity-slideshow-ubuntu/+bug/958880

This is changing two strings.

The first change is the URL for a hyperlink. We include inline HTML
like hyperlinks in translations, so the translation will need to be
updated accordingly.
Original template: "On the mailing list, subscribe on <a
href=\"https://launchpad.net/~lubuntu-desktop\">the page</a>."
New template: "On the mailing list, subscribe on <a
href=\"https://lists.ubuntu.com/mailman/listinfo/Lubuntu-users\">the
page</a>."

The second change is from Synaptic Software Manager to Lubuntu Software Center.
Original template: "Go to the menu, click on System Tools and
<em>Synaptic Software Manager</em>."
New template: "Go to the menu, click on System Tools and <em>Lubuntu
Software Center</em>."

Thank you!
Dylan