DCOR-Aid 0.16.0

This version fixes a performance issue which also caused more requests than needed issued to the DCOR server. In addition, DCOR-Aid now checks for updates during startup.

• feat: check for updates when starting the DCOR-Aid GUI
• fix: when checking resource existence for a dataset, do not call
  "package_show" for every single resource
• fix: use verifiable_files instead of verified_files in error message
  before verifying messages
• fix: possible exception during upload verification with flaky connection
• enh: increase timeout for "package_show" in UploadJob to 500 s
• ref: renamed resource_dict to check_resource_dict in resource_exists
• ref: add optional dataset_dict to resource_exists