Improve pip dependencies parsing

[ghost]

PIP Package dependencies can require additional dependencies for themself:

"requires_dist": [
      "enum34; python_version<\"3.4\"",
      "configparser; python_version<\"3.2\"",
      "pyflakes >= 1.5.0, < 1.7.0",
      "pycodestyle >= 2.0.0, < 2.4.0",
      "mccabe >= 0.6.0, < 0.7.0"
    ],

For example, configparser requires python version < 3.2. Add ability to save system dependencies of package dependencies or create list of system dependencies for whole package.

[romanrostislavovich]

Also, some package has a range of versions from to

[doroxz-zz]

First of all we need to implement this one in dependency schema