Inject ViewModels similar to the Android world

With this merged, there is no need to inject, instantiate and initialize all the view models straight from the application start anymore. I'll add some explanatory comments to key changes in the code.

Closes #99 (closed)

src/main/kotlin/org/briarproject/briar/desktop/contact/add/remote/AddContactDialog.kt

@@ -15,19 +15,18 @@ import androidx.compose.material.Text
 import androidx.compose.material.TextButton
 import androidx.compose.material.TextField
 import androidx.compose.runtime.Composable
-import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
+import org.briarproject.briar.desktop.viewmodel.viewModel
 
 @OptIn(ExperimentalMaterialApi::class)
 @Composable
-fun AddContactDialog(viewModel: AddContactViewModel, onClose: () -> Unit) {
-    LaunchedEffect("fetchHandshake") {
-        // todo: should instead be done automatically as soon as DB is loaded -> in view model
-        viewModel.fetchHandshakeLink()
-    }
+fun AddContactDialog(
+    onClose: () -> Unit,
+    viewModel: AddContactViewModel = viewModel(),
+) {
     AlertDialog(
         onDismissRequest = onClose,
         text = {