fcntl does not work for windows. portalocker might be a better option

[poorvigupta26]

The current locking mechanisms in ConcurrentFileStore, and ProjectManager are not compatible for windows. Changing them to portalocker works, while still keeping the functionality intact. only the function name, fcntl has to be replaced by portalocker. rest all stays the same.

[muellerberndt]

Thanks for pointing that out! Would you like submit a PR?

[poorvigupta26]

Just raised one :)

[muellerberndt]

Merged #45, thanks!