Remove "NULL" in margin of editor in Edit dialog for empty cells

When clicking on a cell with a NULL value while, the Edit dialog
switches into text mode and shows an empty text with "NULL" written in
the line number margin. When then changing to an empty string cell, the
text in the editor did not change (it is still empty after all). This
prevented an action from triggering which meant that the "NULL" text in
the line number marging was not removed.

See issue sqlitebrowser#2204.

Only include the build date for nightly builds.

Our alpha and beta releases use patch numbers greater than 99, so
were being caught by the version string check.

Update version number to 3.11.2

The rebuilt macOS installer (v2) was generated from this tag.

Update version number to 3.11.1

We're using Qt 5.11.3 for the Win64 builds

The DB4S 3.11.0-beta3 Win32/64 & macOS binaries were created from

this commit.

The DB4S 3.11.0-beta2 Win32/64 & macOS binaries were created from thi…

…s commit.

The DB4S 3.11.0-beta1 Win32/64 & macOS binaries were

created from this commit.

This commit is what the DB4S 3.11.0-alpha1 Win32/64 & macOS binaries …

…were created from.