Major refactor to simplify code structure and allow writing to variables

[dvalters]

Includes changes made by @blazk.

Very brief summary:

• Removing stuff that supports mounting directories with multiple netcdf files

• Create NetCDFComponent instance once (instead of for every FUSE operation)

• Open NetCDF file once and pass it as an argument to NetCDFComponent constructor

• Refactor also implements the writing to variable attributes (not yet variables themselves).

• Simple plug-in architecture for generating data representations (probably would need to be further refactored as needed!) Also generating custom text representation is rather slow, needs some sort of optimisation

• Use dependency injection and Composition Root concepts (see main() function in the code)

[dvalters]

(ignoring the Codacy style-test results for now)

Related to #17 #12

[blazk]

thanks @dvalters :) Just to clarify: after this refactoring we can create/update/delete attributes. These operations are not yet implemented for variables!

[dvalters]

Oh yes of course - changed the description now above :)