[FEATURE][BUILD] User can specify the `byzer-notebook-vue` dir

[LiuBodong]

What's the question

• When I use build/build.sh to build this project, I found the script try to download project byzer-notebook-vue from Github and then update the project. But as everyone knows in CN, the GFW limitted download speed from Github, so the download always fails duiring the building.
• What's more is that the script downloads byzer-notebook-vue default to this project's root directory, I think it's not a good idea.
• The last one is that user can decide whether he want to update byzer-notebook-vue

What should we do

• I hope Users cant specify the directory of project byzer-notebook-vue.
• If User not specify the directory, we should use ${project.dir}/../byzer-notebook-vue instead of ${project.dir}/byzer-notebook-vue. That is the two project in the same direcoty
• Add a variable to let user decide whether he want to update byzer-notebook-vue

I am willing to contribute a PR

[allwefantasy]

Maybe we can use path like this: ${project.dir}/.tmp/byzer-notebook-vue and if we build it successfully ,then we can delete .tmp .

It's not a good idea to create a new dir in location which not belongs notebook project.