Consistent interval handling

[rosastern]

In all languages, review handling of intervals and their resolution. This should be consistent across languages, taking into account various differences between languages such as "since" (en) vs. "depuis" (fr) and semantic differences for resolution e.g. "since" (in the past) ≠ "from" (next occurrence).
Consistent default behaviours should also be reviewed and fixed if needed for start and end resolutions depending on start/end grain (e.g. "after x" = "after the end boundary of x").