Add import file bbox/title detection to cmdline renderer

[hholzgra]

The web interface automatically detects the bounding box from import files like GPX and Umap format, and also takes the files embedded title description, if no explicit bounding box or title are given.

The render.py script should do the same, or the functionality should move from maposmatic code into ocitysmap library code so that it's consistent across all frontends.

• [x] Gpx getBounds()
• [x] Gpx getTitle()
• [x] Umap getBounds()
• [x] Umap getTitle()
• [x] Poi getBounds()
• [x] Poi getTitle()
• [x] merge bounding boxes
• [x] add extra margin to bounding boxes
• [x] merge titles
• [x] support legacy file options like --gpx-file?

[hholzgra]

implementation complete