Initial implementation of rtsim2

• Switch to atomic files

• Comprehensive review of implementation, potential performance bottlenecks, etc.

• By opening this merge request, you agree to release your code and all other changes under the GPL 3 license and to abide by the terms set by this license.

• Migrations have been added if applicable

• Significant changes of this merge request have been added to the changelog.

Closes #1476 (closed)