cleanup modules checking code

[AhmadAlsaadi]

dear JJgomera,
I thing this project is quite interesting and I would like to contribute to it. Even though I do not think that I will having much time to contribute regularly to it but I will try to do my best. Below is little description about my first pull request:

I did two things in this pull request:
first I was getting error when I run the program "it is about the global variable in the mainWindow.py file. I went around this error be commenting the global variable there.

second: I tried to shorten the code for checking required and optional modules in pychemqt file.
I used the same procedure that used for the optional modules for the required modules.
I modified the name of set in the tool.depences file from optional_modules to external_modules because I added to this set the data for the required modules.
I did not delete the old code and just comment it and labeled it with "not required anymore"

please let me know if you need further details.

[coveralls]

Coverage remained the same at 24.579% when pulling d7b0cef on AhmadAlsaadi:code_cleanup into e048915 on jjgomera:master.

[codecov-io]

Codecov Report

Merging #14 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #14   +/-   ##
=======================================
  Coverage   36.01%   36.01%           
=======================================
  Files         226      226           
  Lines       32187    32187           
=======================================
  Hits        11591    11591           
  Misses      20596    20596

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[Jeroendevr]

@AhmadAlsaadi Thanks for this pull request. I think this project is interesting also. Is it possible for me to develop/test based on this branch?

[AhmadAlsaadi]

Yes sure.

…

On Mon, 30 Apr 2018, 16:24 Jeroendevr, ***@***.***> wrote: @AhmadAlsaadi <https://github.com/AhmadAlsaadi> Thanks for this pull request. I think this project is interesting also. Is it possible for me to develop/test based on this branch? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#14 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AMiQteg-tnRKST6zm_vt5nC540LUD6fqks5ttxB7gaJpZM4QXV1T> .

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