Clarify "Apply changes" and "Override" tooltips

[lainets]

Clarify that "Apply changes" only compares to the previously fetched configuration without noticing manually made changes, and that override only overrides the fields that were defined in config and does not touch other fields.

[ihalaij1]

I tested some different scenarios.

• I changed the module open date for the aplus-manual overview module in the course settings page. This course has the open date set for the whole course only in the conf.py, the individual modules do not have an open date set.
  • Both buttons override it.
• I changed the points-to-pass for the module in the settings page. This module does not have points-to-pass set in the configuration files.
  • Only the Override button removes the points-to-pass. Apply changes did not change it.

How exactly should we communicate this clearly and concisely in the tooltip? Any ideas for good sentences?