... for ChannelError and APIMisuseError
Before this commit, When rl returns error, we don't know
The actual parameter which caused the error.
By returning parameterised `String` instead of predefined `&'static str`,
We can give a caller improved error message.
TestLogger now has two additional methods
1. `assert_log_contains` which checks the logged messsage
has how many entry which includes the specified string as a substring.
2. `aasert_log_regex` mostly the same with `assert_log_contains`
but it is more flexible that caller specifies regex which has
to be satisfied instead of just a substring.
For regex, tests now includes `regex` as dev-dependency.
This was just an oversight when route calculation was split up into
parts - it makes no sense for get_route to require that we have a
full route message handler, only a network graph (which can always
be accessed from a NetGraphMsgHandler anyway).
This caused a bunch of cascading changes, including
passing loggers down to Channels in function calls
rather than having each Channel have a pointer to the
ChannelManager's Logger (which was a circular reference).
Other structs that the Channel had passed its Logger to also
had their loggers removed. Other newly unused Loggers were
also removed, especially when keeping them would've caused
a bunch of extra test changes to be necessary, e.g. with
the ChainWatchInterfaceUtil's Logger.
