adds stats button on home screen, and creates stats screen, length still needs to be calculated

components/stats.js

@@ -0,0 +1,41 @@
+import React, { Component } from 'react'
+import {
+  View,
+  Text,
+  ScrollView
+} from 'react-native'
+import { LocalDate } from 'js-joda'
+import styles from '../styles/index'
+import cycleModule from '../lib/cycle'
+import getPeriodInfo from '../lib/period-length'
+
+export default class Stats extends Component {
+  constructor(props) {
+    super(props)
+    const lastMensStart = cycleModule().getLastMensesStart(
+      LocalDate.now().toString()
+    )
+    const completedCycles = cycleModule().getCyclesBefore(lastMensStart)
+    this.numberOfCycles = completedCycles.length
+    // TODO get first days, compare with joda
+    const periodLengths = completedCycles.map(cycle => {
+      return cycle.length
+    })
+    // until this point
+    this.periodInfo = getPeriodInfo(periodLengths)
+
+  }
+
+  render() {
+    return (
+      <ScrollView>
+        <Text style={styles.welcome}>based on {this.numberOfCycles} periods:</Text>
+        <Text style={styles.welcome}>min: {this.periodInfo.minimum}</Text>
+        <Text style={styles.welcome}>mean: {this.periodInfo.mean}</Text>
+        <Text style={styles.welcome}>max: {this.periodInfo.maximum}</Text>
+        <Text style={styles.welcome}>median: {this.periodInfo.median}</Text>
+        <Text style={styles.welcome}>standard deviation: {this.periodInfo.stdDeviation}</Text>
+      </ScrollView>
+    )
+  }
+}