Easier string copying

[cohaereo]

Currently, the string list in the tag view only supports copying single strings through the context menu. I'd like to add the following features to the string list:

• Copy string hash through context menu
• Copy string hash by ctrl+clicking the entry
• Copy string value by shift+clicking the entry
• Copy all string hashes+values through a button in the collapsing header

[cohaereo]

Some of these features were added in 68fe256 and a71fd80