Remove threading check and add override flag

Python will always think its in the mainthread, regardless
of if it was started from C via a pthread. You are considered
"off the main thread" when a new thread is spawned from your current
instance. Because there is no way to know whether we started python
with something like jaunch or the terminal, the only way to bypass
the macOS interactive mode block is to introduce an override flag.

src/imagej/__init__.py

@@ -1125,6 +1125,7 @@ def init(
     ij_dir_or_version_or_endpoint=None,
     mode: Union[Mode, str] = Mode.HEADLESS,
     add_legacy=True,
+    override=False,
     headless=None,
 ):
     """Initialize an ImageJ2 environment.
@@ -1183,6 +1184,13 @@ def init(
         the JVM and Python will both terminate when ImageJ closes!
         For further details, see: https://imagej.net/libs/imagej-legacy
 
+    :param override:
+
+        Whether or not to override initialization blocks. If True,
+        unsupported/application breaking behavior, such as interactive mode on
+        macOS, will be possible. If False, initialization blocks preventing
+        unsupported/application breaking behavior are active.
+
     :param headless:
 
         Deprecated. Please use the mode parameter instead.
@@ -1205,7 +1213,7 @@ def init(
 
     macos = sys.platform == "darwin"
 
-    if macos and mode == Mode.INTERACTIVE and _is_main_thread():
+    if macos and mode == Mode.INTERACTIVE and is not override:
         raise EnvironmentError("Sorry, the interactive mode is not available on macOS.")
 
     if not sj.jvm_started():
@@ -1517,14 +1525,6 @@ def _includes_imagej_legacy(items: list):
     return any(item.startswith("net.imagej:imagej-legacy") for item in items)
 
 
-def _is_main_thread():
-    """Detect if on main thread running on the main thread.
-
-    :return: Boolean indicating if the current thread is the main thread.
-    """
-    return threading.current_thread() == threading.main_thread()
-
-
 def _set_ij_env(ij_dir):
     """
     Create a list of required jars and add to the java classpath.