check_inputs: Check shiny inputs
In shutinet/metabSeek: Search in several databases metabolites masses or spectras

Reject an invalid error (custom class error) if any R expression is false also use shinytoastr & shinyFeedback to alert user

1	check_inputs(inputs, exprs, msgs)

`inputs`	vector of character(s) representing name(s) of the input(s)
`exprs`	vector of boolean(s) or vector of R expression(s) which return boolean
`msgs`	vector of string, message(s) to show to the user

## Not run: check_inputs(c("tol", "units"), 
     c(input$tol >= 0, input$units %in% c("mda", "ppm")), 
     c("Tolerance must be positive", "mDa or ppm unit only supported"))
## End(Not run)