Bugfixes and minor improvments

- Detect when we trigger the spamfilter, it's usually just the random
text triggering it.
- Fix delayed spam mode to support prepend/rnd text correctly
- Fix delayed spam mode not handling some errors
- Fix single post mode unchecking Rnd Image
- Set default delay to 1s, it ends up making a post every ~10s, it's way
more efficient than using too many threads and having them timeout/stop
midtransfer