Feature/pass mapped tick to tick format

[DerekMaffett]

Related: FormidableLabs/victory-core#247

Fixes the following issue as well as isolates the logic for tick formatting in chart contexts into a single location. Before it relied on a bunch of branching.

FormidableLabs/victory#585

[boygirl]

Something is going wrong when tickValues are dates:

<VictoryChart style={chartStyle}
            scale={{
              x: "time"
            }}
          >
            <VictoryAxis
              orientation="bottom"
              label={"A LABEL"}
              tickValues={[
                new Date(1980, 1, 1),
                new Date(1990, 1, 1),
                new Date(2000, 1, 1),
                new Date(2010, 1, 1),
                new Date(2020, 1, 1)
              ]}
              tickFormat={(x) => new Date(x).getFullYear()}
            />
            <VictoryLine
              style={{
                data: { stroke: "red", strokeWidth: 5 },
                labels: { fontSize: 12 }
              }}
              label={this.state.label}
              data={[
                { x: new Date(1982, 1, 1), y: 125 },
                { x: new Date(1987, 1, 1), y: 257 },
                { x: new Date(1993, 1, 1), y: 345 },
                { x: new Date(1997, 1, 1), y: 515 },
                { x: new Date(2001, 1, 1), y: 132 },
                { x: new Date(2005, 1, 1), y: 305 },
                { x: new Date(2011, 1, 1), y: 270 },
                { x: new Date(2015, 1, 1), y: 470 }
              ]}
            />
          </VictoryChart>

[DerekMaffett]

@boygirl Ordering issue on the pipeline that was making tickValues override tickFormat. Fixed it.

[boygirl]

@DerekMaffett I'll get this in after doing a release of victory-core