adjust appium image building replacing only appium sources and doing npm install

[vdelendik]

so far we pull appium sources, made edits, build locally and replace compiled js files only.
let's review the process and make sure we override only sources of github module/package and finally do npm install as part of docker image generation.

TBD if we can do a fork and sync with upstream from time to time

[vdelendik]

closing as dupe of #357 where we defined future strategy in building appium image