Handling import of (too) many markers

[elrubio]

When trying to import a large number of markers, an error message tells me that belki is "Refusing to load too many (nnnn) markers".

Probably the limitation exists for performance and/or usability reasons. A look into the code reveals a hard limit of 500 markers.

In the first place, it would be convenient if the error message stated the actual limit. Something like "Refusing to load too many (nnnn) markers. Maximum is 500.". This way the user doesn't have to look up this value in the code.

But maybe the limit could be dealt with somewhat differently? I suggest to either

1. Remove the hard limit but ask the user is it's OK to continue despite potential issues (lag, apparent freezes, etc) if more than LIMIT markers are to be loaded

or

2. Keep the limit in place, load all markers up to LIMIT and inform the user about all three numbers: the limit, the number of markers present in the file and the number of markers that were not loaded.

or

3. Combine both and ask the user something like

   Warning

   You are about to load 2369 markers. Loading more than 500 markers may cause serious performance issues and is not recommended."

   [Load first 500 markers] [Load all markers] [Abort]

[ypnos]

First fix in 0916b5c