dive sites, edit undo, and the major steps towards 4.9

[Berthold Stoeger]

Hi Willem,

On Sonntag, 14. April 2019 10:50:50 CEST Willem Ferguson wrote:

> d) Merge dive sites
> 
> As was apparent in the discussions on this topic I also have many
> duplicate dive sites and they definitely need reorganisation.

If the dive sites have coordinates, you can do this in current master:
- Edit the dive site.
- At the bottom there is a list of "close" sites.
- You can change the value of "close" to something appropriate (e.g. 1000 m).
- Select the sites you want to merge in the list.
- Right mouse click -> merge sites. 

We could extend the list of "close" sites to feature a text filter, if that's 
preferred.

I'll try to remember to add the "close site" thing to the CHANGELOG.

Berthold