Added possibility to use selected text

[tbruckmaier]

Hi,

in order to reference mails from orgmode, I often found myself using the link via thunderlink, and additionally copying part of the message into a quote block:

#+source: [[thunderlink://messageid=123][mail from foo]]
#+begin_quote
... some content from the mail ...
#+end_quote

This CR adds a new placeholder $selected_text$, which contains the selected text by the user. A "link" can be configured like this:

#+source: [[thunderlink://messageid=$msgid$][$subject_filtered$ $author$]]\n#+begin_quote\n$selected_text$\n#+end_quote\n

I have added the cb_thunderlink menu additionally to the right click menu in tabs, as only then we can access the current selection.

Some things I stumbled upon while implementing:

• the right click menu is shown in all tabs, which display /any/ content (for example the addon search). I could not figure out how to limit it to tabs which display a mail. IMHO it's not too bad, but maybe you have an idea about this? This is probably relevant: https://developer.thunderbird.net/add-ons/mailextensions/supported-ui-elements#menu-items
• $selected_text$ is empty if the user uses the message_list menu. I thought about hiding any links with the placeholder from that menu, but thats probably a bit confusing, what do you think?

[CamielBouchier]

Hi, Looks good at first glance. However, currently too short of time to have a decent look. Just wanted to ack though that I will have a look (and merge probably). Camiel B.

[CamielBouchier]

Hi thanks a lot for your contribution. I finally found some time to review and merge. Good stuff! Concerning your questions: I did not find an answer that addresses those issues with limited code (and thus low maintenance). None of it is critical though for using your functionality. It does the job more than decently. Thanks again. Camiel B.