Add troubleshooting help to file upload

[nealhaddaway]

A common problem seems to be occurring at file upload - not using the correct encoding (Mac seems to work the best), so perhaps suggest adding a tooltip or help modal called 'Troubleshooting' with advice on trying a different encoding, saving the file as UTF-8, making sure delimiters and decimals are set correctly...

[DrMattG]

We could also simplify the input process a bit and be strickter on input file type. Does this (#103) work for Mac? Have a look at my branch. If we go this route I need to fix the table as it doesnt like some formats! (grrrrrrrrrrrrr)