Feature: fixed-week behavior

[pdpino]

Fixes #74.

I created a FixedWeekView component, to be used as a fixed timetable showing one week.

Some code is repeated from WeekView, which is not ideal (though I moved most functions to utils.js). I created it this way for two main reasons:

1. If the WeekView component were to be reused, there would be useless virtualized-lists within the component, which is not optimal
2. In the future both components may differ more, and may be useful to have them separated.

If we wanted to avoid code repetition with a new component, instead of creating FixedWeekView as a component of its own, we could add a prop to WeekView such as fixedHorizontally={true/false} (or other name), which would disable horizontal scrolling, plus ensuring the week is displayed starting from monday.

@hoangnm let me know if you prefer a different solution! The PR will be a draft for now.

[hoangnm]

Hi @pdpino, thanks again for your help! I think we can have the prop to prevent horizontal scrolling at the moment unless we have more use cases for the FixedWeekView.

[pdpino]

Ok, sounds good

I will refactor this PR soon!

[pdpino]

@hoangnm I updated the code and marked as ready:

• Added the prop fixedHorizontally and function createFixedWeekDate(), to support the fixed-week behavior
• Deleted the extra FixedWeekView component
• I updated the README with an example of how to use the component as fixed
• I did move some functions to utils, to make the WeekView component smaller (should be easier to mantain) (will do this in a separate PR)

[hoangnm]

Great, I'm merging now.