Function wflow_rename_proj() to rename an existing project

[jdblischak]

If a user wants to change the name of the workflowr project, there are many places that it needs to be changed. Most of the steps can and should be automated! The plan is to write wflow_rename_proj() (open to name suggestions) that does the following:

1. Change name of .Rproj file
2. Change URL of remote repository (need to make sure the protocol stays the same)
3. Change name: and title: in _site.yml
4. Change README title
5. Offer to republish the R Markdown files
6. Offer to rename the project directory itself (and then restart RStudio). Not sure if this is feasible
7. Open the settings page of the existing GitHub repository so that the user can manually rename it

Thanks to @frm1789 and @kbroman for the idea!