Storage Access Framework Compatibility for API 29+

[trife]

https://developer.android.com/preview/privacy/storage
https://stackoverflow.com/questions/58379543/cant-create-directory-in-android-10
https://stackoverflow.com/questions/57116335/environment-getexternalstoragedirectory-deprecated-in-api-level-29-java

[trife]

Utilize the data folder for sample files, etc. similar to OneKK

[chaneylc]

Currently the app uses getExternalStorage() to create a 'Verify' directory. When the app starts it copies sample files to this directory. You will need to replace getExternalStorage() with context.getExternalFilesDir or something alike using SAF.
Read the context documentation which has examples and more explanations: https://developer.android.com/reference/android/content/Context#getExternalFilesDir(java.lang.String)

• Update functionality in MainActivity's onRequestPermissionsResult: this creates a 'Verify' directory which is the root folder for the app. This function copies internal asset files, 'field_sample.csv' and 'verify_pair_sample.csv' to the Verify folder. Although, the current version will not work as explained above.
• Update MainActivity's 'askUserExportFileName' function, this will export the database to a csv file. You will need to replace the usage of Environment.getExternalStorageDirectory() with your SAF implementation. You will need to open a document tree intent, which will let the user choose a folder. Once a folder is chosen, you can create files in that folder. One way to do this with changing minimal code is change getExternalStorageDirectory() to the cache directory, and once the export computation is complete, copy that file to the SAF directory. Alternatively, you can check out https://github.com/PhenoApps/PhenoLib/blob/fb603ef3198c105f537e0e98ac22c387749423a4/phenolib/src/main/java/org/phenoapps/fragments/storage/PhenoLibStorageDefinerFragment.kt#L21 specifically you can use the documentAdvisor class which does the heavy lifting, if you want to use PhenoLib you'll need to add it as a gradle dependency.
• Update importing, (seen in selectDrawerItem function, nav_import case), ACTION_GET_CONTENT lets the user choose a file. Once a file is chosen, it starts the LoaderDBActivity which will parse the file and load it into the local database. Again I think the best strategy is to intercept this uri, copy it to cache as a new file, and then pass the cache file to LoaderDbActivity, that way you don't have to change the implementation.
• The app should work with xlsx, xls, csv, tsv, and txt files. Parsing happens in LoaderDBActivity