Added an option to format numbers using toLocaleString() for table columns

[francesco-cattoglio]

Related to #802

This is the best I could hack, with my limited knowledge and in the time I had to spare. The basic usage is as follows:

• to select which columns should have their numbers formatted according to user locale, you specify them just like you would do for markdown
• there is an extra option that allows you to choose the exact number of decimal digits to be used when formatting, if you need such a precision. This is used for the entire table.

E.G: if you need a table with two columns with numbers formatted using exactly three decimals, and a markdown column with links, you would write

select 'table' as component,
    'links'  as markdown,
    'col A' as number_format_locale,
    'col B' as number_format_locale,
    3 as number_format_digits,
    TRUE as sort;

Pros:

• The changes are very much contained and easy to understand, I do not expect any interference with other features
• Functionality is limited, but can still be useful!

Cons:

• Very limited functionality. toLocaleString() can do so much more, and the list of available options is very very long. I am not sure if we should just allow the user to pass in a JSON structure so that he can choose whatever combination is needed (e.g: this can include formatting with a given currency!)
• no checks w.r.t. the input provided to the number_format_digits field, I have not tested to see what happens if a user inputs anything other than an integer
• when this feature is used, the whole table cell contents are replaced. In 99% of cases this should not be a problem, but I could see someone requesting a way to only format the number and keep the rest of the contents (e.g: keep a currency symbol after the number).

Let me know what you think about this!

[lovasoa]

Thank you very much for this contribution ! I'll take things from here. The results look good, I think I'll revert the logic to be opt out rather than opt in (format numbers by default).