Set default safe mode level #217

Please answer the questions below, it helps us to track the issue.

1. Database version (Ex: PostgreSQL 10.0):
   mysql 5.8
2. TablePlus version (the number on the welcome or about screen, Ex: build 81):
   1.2.1(build 256)
3. Linux distro (Ex: Ubuntu 18.04):
   arch

Currently, the safe mode level has to be set individually for each connection. A default safe mode level setting is needed.
Alternatively, this parameter could be placed in the ~/.tableplus/settings/connections.json file. Currently, it's unclear which file can be modified through a script to achieve this goal.