Replace low level API calls

[villegar]

Opal's developer has suggested replacing low level API calls, and instead use custom R functions.

Here's a list of mappings:

opal.get(o, "project", project, "permissions/resources")
opal.resources_perm(o, project)

opal.get(o, "project", project, "permissions/project")
opal.project_perm(o, project)

opal.get(o, "datasource", project, "tables")
opal.tables(o, project, df=F)

opal.get(o, "project", project, "resources")
opal.resources(o, project, df=F)

opal.get(o, "/system/subject-profiles/")
oadmin.user_profiles(o, df=F)

Reference: obiba/opal#4132 (comment)