ingest kinetic plate-reder files from Tecan i-control

[tp2750]

As discussed over at https://discuss.ropensci.org/t/plate-reader-files/1192/16

Here's a shot at ingesting a plate-reader file from Tecan i-control.

I have tried to follow the guidelines for code-style for the exported function.
It uses some existing functions in a different style. Hope that is OK.

The header data.frame contains fields "Date", "Time", "Start Time" that might look as they should be date-times. They are strings in the Excel-file, and I suspect the format depends on the locale of the computer running i-control, so I chose to leave them as strings.

[jpshanno]

Thanks @tp2750! Everything looks pretty good in the code, I just have to check out why the builds are failing. But we're actually in the process of working out some details about how we deal with reading in the header data and linking it to the data. I am going to let this sit for just a little bit until we get our new approach standardized (shouldn't be too long).

[jpshanno]

Thanks for being patient while we sorted out how we were going to handle temporary files. We've changed it around so that header information is now stored in a temporary file and can be retrieved with the ingest_header() function. The example file's been updated to show that now if there's header info it just needs to be formatted and then run with export_header(). I'm going to be working on the project for most of Wednesday, 11/14, with a zoom line up from at least 10:00 EST - 3:00 EST (https://ucsb.zoom.us/j/966777885). If you are interested in updating what you have done we should be able to get the pull request approved soon.