Demo project missing Maven binaries

[birick1]

Describe the bug
According to Getting started with the Firely SDK CQL repository, building the Demo project is all that is necessary to get going. In particular, a full install of Maven should be present in the repository, and there is a build task called Download CQL to ELM CLI via Maven.

However, the bin folder in the path Demo\Cql\Build\apache-maven-3.8.8\bin\mvn of the build task is not present in the repo. So upon attempting to build, the following error occurs:

To Reproduce
Confirm the Build\apache-maven-3.8.8\bin folder is missing in the repo.

Expected behavior
Add the bin folder to the repo so that a build error does not occur.

Alternatively, list Java (the build task already implicitly assumes java is installed with a correct %PATH%) and Maven as external prerequisites and change the build task to use mvn relying on the %PATH% having been set in the user's operating system. In other words,

1. Change <Exec Command="Build\apache-maven-3.8.8\bin\mvn -f Build\pom.xml dependency:copy-dependencies"></Exec> to <Exec Command="mvn -f Build\pom.xml dependency:copy-dependencies"></Exec>
2. Remove the Demo\Cql\Build\apache-maven-3.8.8 folder and rely on the user to install Maven correctly with %PATH% already set.

[birick1]

Just read through #61 and looks like same root cause as first bullet in that issue.

However, in my case, I am using a Windows machine.

[ewoutkramer]

Yes, this stuff was not checked into the repo in the end due to the git config ;-)

[ewoutkramer]

And it's a pain to get to work on a Mac.

[ewoutkramer]

Fixed in #86.

But not the slashes.

[ewoutkramer]

We'll pick the rest up in #61.