Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)

What kind of change does this PR introduce?

• Cleanup of barely used methods of legacy Logger: Logger.UnformattedWrite, Logger.UnformattedFprintln, Logger.Name, Logger.Flush
• Progress reports of the compilation are now handled via rpc.TaskProgressCB
• Fixed some minor bugs.

What is the current behavior?
No changes in behavior.

What is the new behavior?
No changes in behavior.

Does this PR introduce a breaking change, and is titled accordingly?
A new argument progressCB has been added to commands.Compile, the new function signature is:

func Compile(
	ctx context.Context,
	req *rpc.CompileRequest,
	outStream, errStream io.Writer,
	progressCB commands.TaskProgressCB,
	debug bool
) (r *rpc.CompileResponse, e error) {

if a callback function is provided the Compile command will call it periodically with progress reports
with the percentage of compile completed otherwise, if the parameter is nil, no progress reports will be performed.

Other information:
This PR is the basis for a bigger refactoring aimed to remove the legacy i18n.Logger (#1623).