Comment 6 for bug 1802205

Title: Make all external links in Mahara open in external tab/window by default

Bug Summary: Whether an external <a> link has target=_blank or not we should open them in external tab/window to differentiate mahara site from external content

Acceptance criteria
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1. All external links to be opened in new tab/window by default
2. Except for those that have 'target="_self"'
3. And also have any internal links with 'target="_blank"' to open externally
4. Open them in safe no opener way
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Environment tested: Master
Browser tested: Chrome

Preconditions:
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1. User exists that has access to Group Forum
2. Group exists
3. Forum exists

Test Steps:
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1. Log in as SIte admin
2. Browse to a Group forum
3. Create a new topic Subject = New topic 101
4. In the message WYSIWYG editor - create the following links at the top of the page
-- a. URL = https://www.catalyst.net.nz/ Text to display = catalyst None, Target = None
-- b. URL = https://www.catalyst.net.nz/ Text to display = catalyst same page, Target = same page
-- c. URL = https://www.catalyst.net.nz/ Text to display = catalyst new window, Target = new window
-- d. Existing site page - profile page URL = http://mahara.stevens-lp.dynamic.wgtn.cat-it.co.nz/artefact/internal/index.php Text to display = Profile, Target = None
-- e. Existing site page - profile page URL = http://mahara.stevens-lp.dynamic.wgtn.cat-it.co.nz/artefact/internal/index.php Text to display = Profile, Target = same page
-- f. Existing site page - profile page URL = http://mahara.stevens-lp.dynamic.wgtn.cat-it.co.nz/artefact/internal/index.php Text to display = Profile, Target =new window
5. Enter 8 paragraphs and enter an anchor tag at the bottom of the page
6. create the following links at the top of the page
-- a. URL = #user_cat Text to display = Link to CAT None, Target = None
-- b. URL = #user_cat Text to display = Link to CAT same page, Target = same page
-- c. URL = #user_cat Text to display = Link to CAT new window, Target = new window

Expected result:
--------------------
1. All external links to be opened in new tab/window by default
2. Except for those that have 'target="_self"'
3. And also have any internal links with 'target="_blank"' to open externally
4. Open them in safe no opener way

Actual result: As expected ✔