Feat: create lsl reader and config parser

[MichalSzandar]

• Add LSLReader
• Add ConfigParser - json -> ExperimentConfig (new structure that stores information about device name, montage standard, expected channel count, channels' labels etc.)
• Remove dummy tests
• Update gcovr config (fails below 90% coverage)
• Update readme

Here is an example of config.json file

{
  "config_version": "1.0",
  "device_name": "OpenBCI Cyton 8ch",
  "montage_standard": "10-20",

  "lsl_stream": {
    "name": "obci_eeg1",
    "type": "EEG",
    "source_id": "cyton-a1b2c3",
    "expected_channel_count": 8,
    "expected_sample_rate_hz": 250
  },

  "reference": {
    "label": "linked_mastoids",
    "scheme": "physical"
  },
  "ground": {
    "label": "Fpz"
  },

  "channels": [
    { "index": 0, "label": "Fz",  "enabled": true,  "unit": "microvolts" },
    { "index": 1, "label": "Cz",  "enabled": true,  "unit": "microvolts" },
    { "index": 2, "label": "Pz",  "enabled": true,  "unit": "microvolts" },
    { "index": 3, "label": "Oz",  "enabled": true,  "unit": "microvolts" },
    { "index": 4, "label": "P3",  "enabled": true,  "unit": "microvolts" },
    { "index": 5, "label": "P4",  "enabled": true,  "unit": "microvolts" },
    { "index": 6, "label": "O1",  "enabled": true,  "unit": "microvolts" },
    { "index": 7, "label": "O2",  "enabled": false, "unit": "microvolts" }
  ],

  "impedance_check": {
    "supported": true,
    "threshold_kohm": 5.0
  }
}