Added a function to locally calculate prayer times

[msabur]

Added a function get_prayertimes_local, which tries to be equivalent to the current get_prayertimes function. It uses the Python code from http://praytimes.org/ to compute prayer times. I did only a little testing: I compared prayer times for four cities, and the output was the same with the current function and my function. I used the cities Moscow, Sydney, New York, and Norilsk. I added a dependency, dateutil: https://pypi.org/project/python-dateutil/

Some caveats:

• Not all calculation methods of aladhan.com are included in the code from http://praytimes.org/. They seem easy to add in, but I'm not sure if there will be side-effects.
• I only tested with the ISNA calculation method.
• The new function doesn't store the coordinates/timezone for a given location after getting them from the al-adhan api.

This commit is regarding issue #15

[galacticwarrior9]

جزاك الله خير

I greatly appreciate this contribution. I will take a look at it soon.

[galacticwarrior9]

Looks good to me, thanks again and forgive me for the delay in merging