Add paste-mode to allow multiline text pasting

Ctrl-T toggles paste mode.
Useful when pasting multiline text because it avoids triggering an
enter keypress after linebreaks.
Instead, every \r is translated to \n which is again translated to a
pilcrow (see previous commit).
The pasted text can then be sent as a whole instead of splitting up in
multiple messages.

src/input.c

@@ -262,6 +262,10 @@ bool input_handle(ToxWindow *self, wint_t key, int x, int y, int mx_x, int mx_y)
             force_refresh(self->chatwin->history);
             break;
 
+        case T_KEY_C_T:
+            self->chatwin->pastemode ^= 1;
+            break;
+
         default:
             match = false;
             break;
@@ -278,6 +282,5 @@ bool input_handle(ToxWindow *self, wint_t key, int x, int y, int mx_x, int mx_y)
         match = true;
     }
 
-
     return match;
 }