Add `make_child_app()` and parentApp example package

[lauramaxwell]

Overview

Creates make_child_app() function that copies over relevant pieces of the parentApp (found in inst at the moment...will want to make this a standalone repo eventually) into a new child app. This function also allows the user to include a jobs folder and meta.yaml file either from the parent app or the {matte} templates, and include app-as-package framework elements from golem or rhino, if desired.

closes #16 closes #4 closes #13 closes #6

Test code

Feel free to play with the arguments as you'd like given the help file

 make_child_app(parent_app_dir = "inst/parentApp",
                child_app_dir = "~/childTest",
                copy_jobs_dir = TRUE,
                include_renv = TRUE,
                include_meta_yaml = TRUE,
                job_file_type = "Rmd",
                overwrite = FALSE,
                framework = "none")

devtools::load_all("~/matte/inst/parentApp/")
runApp("~/childTest")

[lauramaxwell]

started a template for the R/main.R file needed for rhino child apps, but still needs some work. golem and no-framework child apps are working well on my end.

[jiwanheo]

I think we'd want to put in a Rproj when we create new children.

When overwriting, we should print out a message? (it does overwrite) Honestly, we can just disable overwrite?

In this else clause, system.file can't start with "inst". You can actually omit "inst", and just give it the file name

I think we decided to detect the yaml file usage from parent? This might have to be tweaked

[lauramaxwell]

first two comments make sense i can i fix those quickly.

for the yaml usage- if they select to copy the jobs folder from the parent and a yaml exists in the parent's jobs folder than it will get copied over instead of the yaml template, which is i think what we wanted. maybe we need to make this more explicit in the documentation or argument names?