Bug 1620789 - Add source code download and build instructions to the website - fix links. r=me

src/dev/code-development.en.html

@@ -93,7 +93,7 @@ commands:
 <pre><code>
    git clone https://gitlab.com/seamonkey-project/seamonkey-2.53-mozilla.git mozilla-253<br>
    cd mozilla-253<br>
-   git clone https://gitlab.com/seamonkey-project/seamonkey-2.53-comm.git comm
+   git clone https://gitlab.com/seamonkey-project/seamonkey-2.53-comm.git comm<br>
    cd extensions<br>
    hg clone https://hg.mozilla.org/chatzilla irc<br>
    hg clone https://hg.mozilla.org/dom-inspector inspector<br>

src/dev/index.en.html

@@ -29,7 +29,7 @@ If you want to help, you can find some resources here.
 
 <p>Our <a href="get-involved">Getting Involved with SeaMonkey</a>
 page is another good entry point to helping out our project, as well as the
-<a href="http://wiki.mozilla.org/SeaMonkey:Home_Page">SeaMonkey pages on the
+<a href="https://wiki.mozilla.org/SeaMonkey:Home_Page">SeaMonkey pages on the
 Mozilla wiki</a> - and the
 <a href="https://blog.seamonkey-project.org/">SeaMonkey blog</a> features
 development news every now and then.
@@ -53,8 +53,7 @@ Localization</a> wiki page.
 Testing our code is a very major and important task in every software project,
 and the good thing is that anyone can participate in that by downloading
 <a href="nightly">"Nightly" builds</a>, using them and
-<a href="http://developer.mozilla.org/en/docs/Bug_writing_guidelines">reporting
-bugs</a>.
+<a href="https://developer.mozilla.org/en-US/docs/Mozilla/QA/Bug_writing_guidelines">reporting bugs</a>.
 </p>
 
 <p>
@@ -72,12 +71,10 @@ code you're testing might not have been tested at all before.
 </p>
 
 <p>
-Our <a href="get-involved">Getting Involved</a> page, the Mozilla wiki on
-<a href="http://wiki.mozilla.org/SeaMonkey:QA">SeaMonkey QA</a> (Quality
-Assurance) and the MDC (Mozilla Developer Center)
-<a href="http://developer.mozilla.org/en/docs/QA">QA section</a> offer some
-good additional info about testing and helping us improve our software quality
-through that.
+Our <a href="get-involved">Getting Involved</a> page and the Mozilla wiki on
+<a href="https://wiki.mozilla.org/SeaMonkey:QA">SeaMonkey QA</a> (Quality
+Assurance) offer some good additional info about testing and helping us improve
+our software quality through that.
 </p>
 
 <h2 id="marketing">Marketing And Other Contributions</h2>
@@ -96,7 +93,7 @@ people to SeaMonkey, as that is explicitly allowed by our
 
 <p>
 The merchandise available from the
-<a href="http://www.zazzle.com/seamonkeyproject">SeaMonkey shop</a> can also
+<a href="https://www.zazzle.com/seamonkeyproject">SeaMonkey shop</a> can also
 help you in spreading the word.
 </p>