Add plot_cesium_drift_from_jobspec.py
Add plot_cesium_drift_from_jobspec.py

Script used during LLO 2018 trip to plot cesium drift for cesium clock
calibration. Based off of an earlier outdated script, updated to work with
geco_gwpy_dump and its jobspecs.

Jobspec used (contains redundant info not used by this script):

{
  "start": "Sat Jan 20 00:00:00 2018",
  "end": "Sun May 20 00:00:00 2018",
  "exts": ["hdf5"],
  "max_chunk_length": 86400,
  "channels": [
    "L1:SYS-TIMING_C_MA_A_PORT_2_SLAVE_CFC_TIMEDIFF_1"
  ],
  "trends": [
    ".mean,m-trend"
  ],
  "dq_flags": [],
  "max_chunk_length": 86400,
  "slow_channel_plots": {
    "height": 10.0,
    "width": 7.5,
    "channel_descriptions": {
      "L1:SYS-TIMING_C_MA_A_PORT_2_SLAVE_CFC_TIMEDIFF_1": "LLO Cs-III Cesium Clock"
    },
    "plots": [
      {
        "plot_properties": {
          "detrend": "none",
          "#handle_missing_values": "hide",
          "#handle_unrecorded_values": "hide",
          "omitted_indices": [],
          "outliers_lower_bound": -1e-5,
          "outliers_upper_bound":  1e-5,
          "fname_desc": "original-data"
        },
        "dq_flag": null,
        "channel": "L1:SYS-TIMING_C_MA_A_PORT_2_SLAVE_CFC_TIMEDIFF_1"
      },
      {
        "plot_properties": {
          "detrend": "linear",
          "#handle_missing_values": "hide",
          "#handle_unrecorded_values": "hide",
          "omitted_indices": [],
          "outliers_lower_bound": -1e-5,
          "outliers_upper_bound":  1e-5,
          "ylim_top": 220,
          "ylim_bottom": -220
        },
        "dq_flag": null,
        "channel": "L1:SYS-TIMING_C_MA_A_PORT_2_SLAVE_CFC_TIMEDIFF_1"
      }
    ],
    "run": "post-O2"
  }
}

stefco/geco_data,stefco/geco_data,stefco/geco_data