Convert rc.verbose config variable into separate vars

Currently, we use `verbose` configuration variable to set the list of verbosity tokens that control what kinds of messages are displayed by `task`:

```
verbose=blank,header,footnote,label,new-id,affected,edit,special,project,sync,filter,unwait,override,recur
```

However, once user tries to customize this list of tokens, they have essentially froze their configuration, unable to get new verbosity tokens that come as defaults in future versions. Instead, we should decompose the list of the verbosity tokens into their own verbosity variables:

```
verbose.blank=1
verbose.header=1
...
```