Introduce update_from_pandas method for ui.table

[tmlmt]

Resolves: #2731

Opening this PR as draft to request a check as to whether this is going in the right direction.

Principles followed:

• In order to reuse the part of the code which checks the DataFrame and potentially casts into string the special types, took it out of the from_pandas method and even out of the class to avoid it being confused with a class method. Alternative is to keep it in the class with one or two leading underscores in the name.
• Only expect a DataFrame to be given as parameter, the rest can be updated manually relatively easily (I though intend to update this PR if you accept the introduction of Allow pandas DataFrame df and rows as two sources of rows, make columns optional, and introduce default column config #3263 which enables a finer grain of definition of the columns upon calling the function). Alternative is to accept some of same other parameters as in from_pandas

[falkoschindler]

This feature has been developed further in PR #3525 and will be released shortly in version 2.0.0.
Therefore I'll close this pull request.