Show a useful icon in SQL tabs (sqlitebrowser#2153)

The icon shows whether the tab is linked to a project file (open_sql icon)
or to a file in disk (document_open icon).

This has a lateral effect of fixing this, since the tab always has an icon
and the height of the tab bar never changes:

sqlitebrowser#2073 (comment)

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.