Make User-Agent string customizable

[Simon-Will]

This should resolve issue #36.

I tried to use the same underscore names you are using. Not sure if I succeeded, though, since I didn’t fully understand your usage, to be honest.

[Simon-Will]

I just noticed that I mistakenly included another commit in my master branch. Only the first of the two commits should be merged in this request. (Although the other commit may also be a reasonable change.) So I just reverted the second commit in my master branch.

[mocnik-science]

Dear Simon,

Thank you very much for your appreciated help. I double checked the usage policies of the various services used by OSMPythonTools. It makes sense to add a user specified part to the user agent string.

Still, I did not merge directly but rather rewrote your code due to several reasons:

• There were unnecessary commits contained in the merge request.
• The commit message did not align well to the others.
• There is no reason to not assemble the user agent string in the _userAgent method, as was done before. Shifting this to the __init__ function is not intended.
• The use of OSMPythonTools can be 'on the edge'. Nominatim, for instance, is very strict with unacceptable use. In order to make finding issues easier for the operators of these services and to prevent situations where the user of OSMPythonTools just overwrites the user agent string with an empty one, I prefer to only add the user-specific part to the default user agent proposed by OSMPythonTools.

I hope you agree to my decisions. It took some time, but some more thinking was necessary to resolve this request in a suitable way.

Best!

[Simon-Will]

Hi,

I fully agree with your decisions. They are very reasonable.

Kind regards
Simon