add decision- and blocking-functions to repl, cleanup (#2258)

* deprecate mostly unused dc_get_blocked_cnt() api

instead, the size returned by get_blocked_contacts() should be checked,
this is safer and allows easier adaption of blocking rules.

ui or python seems not to use dc_get_blocked_cnt(),
however, there is one test in node,
therefore, the function will continue working for now
(by just returning Contact::get_all_blocked().len() then)

* add decision api to repl tool

* add block/unblock api to repl tool

* unify usage of @deprecated doxygen command

deltachat-ffi/src/lib.rs

@@ -1640,7 +1640,7 @@ pub unsafe extern "C" fn dc_get_blocked_cnt(context: *mut dc_context_t) -> libc:
     }
     let ctx = &*context;
 
-    block_on(Contact::get_blocked_cnt(&ctx)) as libc::c_int
+    block_on(async move { Contact::get_all_blocked(&ctx).await.len() as libc::c_int })
 }
 
 #[no_mangle]