4.5.2

[Dirk Hohndel]

Just a quick heads up. Heinrichs Weikamp surprised us with a firmware change that breaks downloading from their dive computers. It would have been nice had we known this was coming, but it is what it is. I decided to merge Jef's latest updates to libdivecomputer (YAY Jef!!!) into our branch and respin Subsurface as 4.5.2 using the updated libdivecomputer.

I'll also use this opportunity to make a first AppImage available - let's see if people are interested in this.

Most binaries are ready, I'll announce this shortly on our website, FB, G+, etc.

/D