Drop case-sensitive transformation and resolve dependency issues

[jonocarroll]

I wasn't able to run use_datadriven_cv() because files are case-sensitive on linux so the templates weren't being found.

This PR removes that transformation and keeps the .R/Rmd casing.

Additionally, resolves the dependency issue with icon and googlesheets4, so closes #60 closes #69 closes #73 closes #77 incorporating all the changes in those.

All tests pass on linux (x86_64-pc-linux-gnu R version 4.1.2 (2021-11-01)) but not tested on other platforms.

I'm also able to generate a CV with these changes. Thanks for this package!

[fthielen]

Hi, I get the following:

> devtools::install_github("nstrayer/datadrivencv#83")
Downloading GitHub repo jonocarroll/datadrivencv@master
Error: Failed to install 'datadrivencv' from GitHub:
  Missing commas separating Remotes: 'ropenscilabs/icon
    mitchelloharawild/icons'

But the following worked for me:

devtools::install_github("nstrayer/datadrivencv#69")

[jonocarroll]

Thanks @fthielen - I updated my PR to fix that. This PR also has some additional changes on top of PR 69.