Remove close buttons on tabs and add button for closing SQL tabs

This gives us some more space in the tab bar and should reduce the risk
of accidentally closing a tab. It looks prettier too. We could add an
option for this in the Preferences dialog but in order to not add too
many rarely used options, let's try it without an option first.

See issue sqlitebrowser#1968.

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.

Update version numbers to 3.10.1