Feature request: Allow numeric sample ids in front end

[danlooo]

The front end will crash if all values in column sample_id of the sample meta data table were numeric. The back ends seems to work after 8b50a25. However, the front end uses implicit type inferring by default but the sample meta data object has a more explicit column type inferring as implemented in danielLib/R/guess_coltypes.R. This result in type compatibility errors in joining tables.

A note in params.csv of the data base was set to allow only sample ids starting with a character. Debugging is hard because shiny does not provide line numbers and file names of the errors.