Add pen color selection

[serpilliere]

This PR adds the feature of choosing color from the menu.
Fix #71

[bk138]

Thanks for the contribution! This does not work for me yet, though: The dialog pops up, I can choose a colour, but the painting colour stays red... Any idea what to do/look at?

[serpilliere]

Oh! Interesting.
Can you add a printf("test\n"); at line 602, just after the:

      gdk_cairo_set_source_rgba(data->default_pen->paint_ctx, data->default_pen->paint_color);

If should display "test" after you validate the color.
It's to validate all the callback color selector

[bk138]

Yeah, that fires.

[serpilliere]

Thank you for the feed back @bk138 !
This means I missed something in setting the color back to the pen...

[bk138]

Might this relate to differing gtk versions?

[serpilliere]

I just realized that using the default branch, I cannot erase using right or middle button.
This may be linked to this (I tested on arch linux)

[serpilliere]

Ok, I manage to reproduce the bug: I forgot to set a configuration file. This explains that I wasn't able to erase using right click.
I am debugging the branch now I have reproduced the bug

[serpilliere]

Hi!
It seems that the different tools are stored in a hash table, and the way to get them is to know their shortcut 😢
So I added a pointer to the current tool, which is update each time the user select a different tool.
Now, the color may change the current tool !
The color is not stored back to the config file.

[bk138]

Some of this can be used for #110, so I'd like to keep a reference once work starts on that. Closing as this PR will not be merged as-is, but code will be re-used.

[serpilliere]

Great!