Use list preference for chart x axis settings

MyTracks/res/values/arrays_do_not_translate.xml

@@ -92,6 +92,14 @@ limitations under the License.
     <item>15</item>
     <item>-1</item>
   </string-array>
+  <string-array name="chart_x_axis_options">
+    <item>@string/settings_chart_by_distance</item>
+    <item>@string/settings_chart_by_time</item>
+  </string-array>
+  <string-array name="chart_x_axis_values">
+    <item>@string/chart_x_axis_distance</item>
+    <item>@string/chart_x_axis_time</item>
+  </string-array>
   <string-array name="frequency_values">
     <item>0</item>
     <item>1</item>

MyTracks/res/values/do_not_translate.xml

@@ -16,6 +16,8 @@ limitations under the License.
 -->
 <resources>
   <!-- DO NOT TRANSLATE ANY STRINGS IN THIS FILE. -->
+  <string name="chart_x_axis_distance">DISTANCE</string>
+  <string name="chart_x_axis_time">TIME</string>
   <string name="eula_korean">위치정보서비스 및 위치기반서비스 이용약관\n
 \n
 다음은 구글코리아 유한회사(이하 “Google”)가 Google의 제품에 대하여 제공하고 있는 위치기반서비스에 적용되는 이용조건입니다. 아래 이용조건은 이동통신사업자의 가입신청서에 포함된 위치정보 수집동의 및 모바일 단말기 이용조건과 함께 적용됩니다.\n

MyTracks/res/values/keys.xml

@@ -18,12 +18,12 @@ limitations under the License.
   <!-- Keys for persisted preferences. Sorted alphabetically. DO NOT TRANSLATE. -->
   <string name="allow_access_key">allowAccess</string>
   <string name="auto_resume_track_timeout_key">autoResumeTrackTimeout</string>
-  <string name="chart_by_distance_key">chartByDistance</string>
   <string name="chart_show_cadence_key">chartShowCadence</string>
   <string name="chart_show_elevation_key">chartShowElevation</string>
   <string name="chart_show_heart_rate_key">chartShowHeartRate</string>
   <string name="chart_show_power_key">chartShowPower</string>
   <string name="chart_show_speed_key">chartShowSpeed</string>
+  <string name="chart_x_axis_key">chartXAxis</string>
   <string name="default_activity_key">defaultActivity</string>
   <string name="export_external_storage_format_key">exportExternalStorageFormat</string>
   <string name="export_google_fusion_tables_public_key">exportGoogleFusionTablesPublic</string>