it should be possible to run the package without pypest / amici

[fbergmann]

I needed the following changes to have the package run for me:

diff --git a/petab_timecourse/__init__.py b/petab_timecourse/__init__.py
index 4f77a5b..b38cd07 100644
--- a/petab_timecourse/__init__.py
+++ b/petab_timecourse/__init__.py
@@ -22,14 +22,17 @@ from .misc import (
 )
 
 
-from . import amici
-from .amici import (
-    simulate_timecourse,
-)
-
-from .pypesto import (
-    TimecourseObjective,
-)
+try: 
+    from . import amici
+    from .amici import (
+        simulate_timecourse,
+    )
+
+    from .pypesto import (
+        TimecourseObjective,
+    )
+except ImportError:
+    pass
 
 from .problem import Problem
 
diff --git a/petab_timecourse/simulator.py b/petab_timecourse/simulator.py
index fb7a9bf..249b06d 100644
--- a/petab_timecourse/simulator.py
+++ b/petab_timecourse/simulator.py
@@ -23,11 +23,15 @@ from petab.C import (
 from .C import (
     PERIODS,
 )
-from .amici import (
-    precreate_edata_periods,
-    precreate_parameter_mapping_periods,
-    add_output_timepoints_if_missing,
-)
+try:
+    from .amici import (
+        precreate_edata_periods,
+        precreate_parameter_mapping_periods,
+        add_output_timepoints_if_missing,
+    )
+except ImportError:
+    pass
+
 from .misc import (
     get_timecourse,
     subset_petab_problem,