Allow sorting by clickin the entire header

[TheLudd]

This adds the class columnSorting to the div inside the table headers
which will allow the user to sort the columns by clicking the entire
header. Before this commit, the user was forced to click on the header
text for the sorting to take effect.

[TheLudd]

IMHO, being able to click the entire header to sort is a better user experience, therefore this change.

I only added one test to make sure that sorting actually works. The sorting plugin is already extensively tested and it seems unnecessary to duplicate all tests for this. All the previous tests still pass.

[AMBudnik]

Great idea, let us take a closer look.

[TheLudd]

Just noticed that there was a merge conflict so I did a rebase. The conflict was in the files in the dist folder. I read in the contribution guidelines that I should edit files in the src directory and then do a build. Is this correct? I could just skip doing the build and there would have been no conflict.

[krzysztofspilka]

I'm marking this one as a feature request as it demands a deep changes in the standard behaviour of our current sorting functionality.

To be found here: https://github.com/handsontable/handsontable/wiki/Feature-requests

[TheLudd]

@krzysztofspilka What is the deep change? Did the implementation I provided cause any problems?

[AMBudnik]

I'm transferring this issue into a Github Discussion #7990. Please feel welcomed to share your comments and propositions on this change.