Some opinionated improvements

[daniele-athome]

Hello there!!
Thanks for this simple but quite powerful app! I've been using it for a few days now and I've made some (in my opinion) improvements that I would like to share. But before opening a few PRs I'd like to know if you'd be interested:

• history entry tap highlight ("ripple effect") on both single tap and long tap (activated state)
• taller history entry (in theory the minimum touch area for Google should be 48dp... I've been testing 40dp for now... let me know what you think)
• use a time picker for the start time in edit entry dialog (actually I put a button in place of the text field: when you click it, the time picker replaces the button; details in commit - If you have better ideas I'm all ears of course)
• upgrade Rx stuff to latest minor version
• minor fixes and optimizations (mainly some warnings and layout optimizations, dependencies upgrades, nothing fancy really)

I'll soon be working also on app shortcuts - I don't know when exactly, sorry.

I think I will also work on storage access framework for Android 11 (as a matter of fact I've incremented the targetSdkVersion but I have Android 9 so I'm not really affected for now) but I don't know when yet.

[daniele-athome]

More stuff:

• area chart: avoid showing a cliff when selecting a past end date (I don't know if I did this right though: daniele-athome/chronofile@4bd4be6)
• fix menu item background (enabling the standard tap effect)