[GRASS-git] [OSGeo/grass] b9575e: g.gui.timeline: improve missing package msg

[Markus Neteler]

  Branch: refs/heads/master
  Home:   https://github.com/OSGeo/grass
  Commit: b9575e542da054592e00686e94182a22ce2bc353
      https://github.com/OSGeo/grass/commit/b9575e542da054592e00686e94182a22ce2bc353
  Author: Markus Neteler <neteler at gmail.com>
  Date:   2020-07-25 (Sat, 25 Jul 2020)

  Changed paths:
    M gui/wxpython/timeline/frame.py

  Log Message:
  -----------
  g.gui.timeline: improve missing package msg

Be less obscure with the error:

```
Unable to start Timeline Tool.
Reason: The Timeline Tool needs the "matplotlib" (python-rmatplotlib)
package to be installed. No module named
‘mmatplotlib.backends.backend_wxagg'
...
```