Added cog for fitness activity logging feature.

At its starting state it would accept following commands:
- !getunits <activity>: Would send a JSON file with activity units via Discord message. Those files are responsible for setting up a fitness activity to log.
- !getlog <activity>: Would send a CSV file with fitness activity log. Those files contain records with timestamp, username, and reported activity measurements.
- !<activity> <value> <unit (optional)>: Would create a record with your fitness activity in corresponding CSV log file. If you choose to report different unit (feet, for example), it is going to convert as specified in its corresponding JSON file with units (to meters, for example) if the activity specified as convertable. Non-convertable activities' units are ignored.

fitnessCog/activities/climb.json

@@ -0,0 +1,48 @@
+{
+    "convertable": true,
+    "units": {
+        "meter": {
+            "factor": 1,
+            "aliases": [
+                "meter",
+                "meters",
+                "m",
+                "m."
+            ]
+        },
+        "kilometer": {
+            "factor": 1000,
+            "aliases": [
+                "kilometer",
+                "kilometers",
+                "km",
+                "km."
+            ]
+        },
+        "foot": {
+            "factor": 0.3048,
+            "aliases": [
+                "foot",
+                "feet",
+                "ft",
+                "ft."
+            ]
+        },
+        "mile": {
+            "factor": 1609.344,
+            "aliases": [
+                "mile",
+                "miles",
+                "mi",
+                "mi."
+            ]
+        },
+        "step": {
+            "factor": 0.18,
+            "aliases": [
+                "step",
+                "steps"
+            ]
+        }
+    }
+}

fitnessCog/activities/pushups.json

@@ -0,0 +1,3 @@
+{
+  "convertable": false
+}