Support SDF-format for Indigo-Ketcher API

[even1024]

Background
Ketcher should support SDF import and export along with other formats

Solution
As Indigo supports SDF import and export it's necessary to add corresponding functionality into indigo service API and Indigo wasm module. Every chemical structure fragment should be converted as a separate molecule in SDF.
As SDF can have a set of properties for every MOL-fragment it's necessary to save it in KET in a form of an array in the molN block:

"mol0": {
"properties": [
    { "key": "key1", "value": "value1"},
    { "key": "key2", "value": "value2"},
    { "key": "key3", "value": "value3"}
]
}