Parameterise Usage Help of CliApplication

[aslesarenko]

Problem

Currently the following places are hard coded:

val BaseDocUrl = "https://ergoplatform.github.io/ergo-tool/api"

Usage Syntax:\tergo-tool $name ${cmdParamSyntax}

Thus:

• api url shown by HelpCmd command is incorrect for dex commands
• usage syntax have incorrect name of executable

Solution

• transform BaseDocUrl into abstract method def baseDocUrl: String in CmdDescriptor
• Implement baseDocUrl ergo-dex#7
• introduce def launcher: String method to use in Usage Syntax above.