Change plugin schema: Switch version to String instead of Number

[mStirner]

backend/components/plugins/class.plugin.js

Line 64 in d17066b

version: Joi.number().required(),

Switch from Number, to String, which represents a semver version.

• https://semver.org/#is-there-a-suggested-regular-expression-regex-to-check-a-semver-string
• https://gist.github.com/jhorsman/62eeea161a13b80e39f5249281e17c39

[mStirner]

Switch package.json from string property to object, like this

openhaus:{
  backend: ">=3.0.1 || <=2.5.32",
  connector: ">5.2"
  frontend: "<=2.1 || >=2.4"
}