ReleaseNotes: start preparing for 4.8 / 2.1

Move changes from CHANGELOG to ReleaseNotes and add a few items that
were missing.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

ReleaseNotes/ReleaseNotes.txt

@@ -2,6 +2,45 @@
 
 = _Subsurface_ Release Notes
 
+New in _Subsurface_ 4.8
+~~~~~~~~~~~~~~~~~~~~~~~
+
+- Desktop: fix crash on manual addition of dive to fresh logbook
+- Desktop: fix showing of the manual
+- Desktop: don't save empty file to cloud [#1228]
+- Desktop: allow editing from list-view [#1213]
+- Desktop: don't add six seconds to dive duration [#554]
+- Desktop: fix manual editing of dive duration [#1211]
+- Desktop: implement bailout events in logbook and planner
+- Desktop: fix time format in main tab [#1234]
+- Desktop: various bugfixes and improvements for dive picture handling
+- Desktop: fix output of ICD-notes in planner
+- Desktop: add information about actual isobaric counter diffusion happening
+- Desktop: fix several issue when manually editing dive profiles
+- Equipment: fix bug with the maximum number of allowed tanks [#1401]
+- Shearwater import: include DC reported ceiling
+- Suunto DM import: improved temperature parsing in special cases
+- CSV import: allow newline ('\n') in notes field
+- BLE support: fix several issues with BLE download both on desktop
+  (Mac/Linux) and mobile
+- Mobile: fix potential crash when editing manually added dives [#1408]
+- Mobile: fix missing profiles when manually adding dives or editing such
+  dives [#1419]
+- Mobile: when transitioning from NoCloud mode to cloud storage, keep
+  the dives already stored locally [#1404]
+- Mobile: add cloud storage user name to global drawer banner
+- Mobile: add button to About page to copy logs to clipboard; this makes it
+  easier to provide the required information when reporting issues
+- Mobile/iOS: adjusted launch page to be centered
+- Mobile: adjusted size of About page for small screen (no scrolling)
+- Mobile: download page now remembers last used connection
+- Mobile: recalculate derived values after dive edit
+- Mobile: fold dive trips to give better overview for large dive lists
+- Mobile: fix using current GPS position when editing or adding dives
+- Mobile: fix broken FTDI download on Android devices that allow us access
+  to their /dev directory (still, many devices don't support the way
+  Subsurface-mobile accesses USB devices via OTG adapters)
+
 New in _Subsurface_ 4.7.8
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 - Desktop: Add Tags column in dive list view