Read and write a model's tasks to config files

[alex-simm]

What

When a model is written to or read from a configuration file, the tasks are formatted and parsed, too.

Why

Fixes #18

How

Almost the same as it is done for the qubits and couplings in a model. There's a list of possible classes in tasks.py:task_lib and instances are created by passing the parsed dictionaries to the classes' constructors in the params argument. As far as I can see, adding that argument doesn't create any conflict with the normal usage of the constructors.

[codecov]

Codecov Report

Merging #116 (4717124) into dev (31e96be) will increase coverage by 0.16%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##              dev     #116      +/-   ##
==========================================
+ Coverage   58.44%   58.61%   +0.16%     
==========================================
  Files          36       36              
  Lines        5304     5325      +21     
==========================================
+ Hits         3100     3121      +21     
  Misses       2204     2204              

Impacted Files	Coverage Δ
c3/libraries/tasks.py	54.83% <88.23%> (+9.55%)	⬆️
c3/model.py	73.88% <92.30%> (+0.70%)	⬆️

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[lazyoracle]

@alex-simm I pushed some commits to fix the failing tests (as explained by @nwittler). I think this PR is ready to be merged now. Please remember to do a git pull before making further changes to this branch to incorporate my commits in your local repo.

[lazyoracle]

Ready to merge!

[alex-simm]

@alex-simm I pushed some commits to fix the failing tests (as explained by @nwittler). I think this PR is ready to be merged now. Please remember to do a git pull before making further changes to this branch to incorporate my commits in your local repo.

[alex-simm]

Great thanks, I didn't notice the other test was failing.

[alex-simm]

Do the codeclimate issues need to be fixed? The fromdict function doesn't look too complex for me.

[lazyoracle]

Do the codeclimate issues need to be fixed? The fromdict function doesn't look too complex for me.

No they aren't a result of your edits, so I guess we fix them some other time.