Make console completion case-insensitive

* ConsoleField: replace the case by the one of the completed arg
* String: add case-insensitive versions of prefix functions
* LineEditData: add a "times" argument to Delete and Move functions

Completion is case-insensitive but the actual cvars/commands/... still are case sensitive (do we want this ?)
Log: add Log::{Error,Warn,Notice,Debug} for when we need temporary prints