Support standard text files in ACC Docs

[MiWolff]

To add more detailed information than would befit the description of a file, you obviously still need to rely on an office document when a text file would actually suffice. I propose to allow for some basic text editing and a 'view' feature for text files. Text editing cannot be a problem because there already is an editor in place when fiddling with notes or issues.

[R.Robert.Bell_Seagen]

I use Readme.txt files all the time. Not being able to view them, much less not being able to edit them, is unfortunate.