Make DefaultLUTService use IOService

`DefaultLUTService.legacyTextLUT` uses `TableLoader.valuesFromTextFile` to read a LUT from a CSV files. Since this is the only use of `TableLoader.valuesFromTextFile` in our codebase we should retire it in favor of implementations in `scijava-plugins-io-table`. See also https://github.com/scijava/scijava-plugins-io-table/issues/4#issuecomment-452479079.

This, however, poses several challenges/tasks (in no particular order):
1. Should `LUTService` still support reading of LUTs from `InputStream`? If so, such requests can't be handled by `IOService`. Is that correct, @ctrueden?
2. We should migrate code for reading LUTs from `InputStream`s into dedicated `IOPlugin`s
3. Basically, strip down the `LUTService` to pass requests to `IOService` and fail gracefully if a LUT can't be read (which doesn't work for `InputStream`s - see 1.)

Start at DefaultLUTService.legacyTextLUT and trace its use of TableLoader.valuesFromTextFile, then review the linked scijava-plugins-io-table discussion. Resolve whether InputStream support remains and how IOService and dedicated IOPlugins should handle LUT reads before defining completion criteria.

Written by the indexing model from the issue text.