style(mtrl): start migration to materiel design

Target to v21 android sdk
Add new star style
General major resources cleanup

Relative to #81
fix: actionbar not visibile in about view

Close #82
fix: actionbar not visible in preference view

Close #83
style(mtrl): improve prefs slider appareance
feat(list): use swipe refresh layout

Replace legacy pullToRefresh

Relative to #81
feat(mtrl): use snackbar to provide feedback

Replace toast by snackbar
Add snackbar library

Close #84
style: change map & list icons

Relative to #81
feat(map): increase map zoom level

Close #85
refactor(xml): replace sax parser by jsoup

Close #80
style(list): add some margin to make list clearer

Relative to #81
style(about): add version in about section and minor changes
style(map): change the location button style

Button has round borders & does not have the stock style anymore
Add some margin

Relative to #81
feat(list): click on a station should display more info

An activity is opened with the station info (name, address, bikes, ...)
Upgrade to droidparts:2.6.2

Close #86
chore: upgrade android support version

Relatie to #81
style(launcher): update app launcher icon

Relative to #81
style: remove unused image resources

Relative to #81
style: change last update time preference label

Use shorter label: 'update time'
style(about): add logo under the app title
fix(station): update process throws android.database.sqlite.SQLiteConstraintException

Close #87
fix(update): the stations update always change the last update time in settings

Check if there are really new stations added

Close #88