Sailfish: Switch out SilicaWebview for SailfishWebview

[Thaodan]

This change replaces the WebKit based Webview witha Gecko based Webview. Busyindicator is not needed since SailishWebview provides its own.

WIP because:

• PulleyMenu doesn't work right now
• Navigation between the opened and the last opened page doesn't work

[Thaodan]

Only the last commit is part of this PR, the rest is part of #86.

[Thaodan]

Status update:

WebViewPage

• I incorporated the changes from #93, navigation works fine when the Sailfish.WebView is contained inside a SilicaFlickable. Including the change the commit works fine. Thanks @tsyesika. (I can add as signoff since I picked parts of your commit and the smashed them together)

SignInPage

What works:

• The page loads and the redirection works fine.
• Login works
• the password popup is disabled.

What doesn't:

• ~Check to grab url Currently the page tries to grab the url after it is the final OAuth url. This is somewhat a hack since sites usually want to redirect to a local http address to accept the token. A good candidate for that would be an oauth lib such as amberwebauthorization however I'm not exactly sure. I need to find the equivalent of the urlchanged signal in Sailfish WebView.~
• The package header doesn't show
• ~the password popup isn't disabled.~

[Thaodan]

@accumulator: What kind of redirect url are you using?

[Thaodan]

Status Update

The page has been rewritten with a Sailfish WebView element instead of a SilicaWebview.

To adjust the page, improve the layout and work better with the Sailfish WebView I replaced the AbstractPage with Dialog. The page was more of a dialog in any case, the reload option was redundant.

While doing so I replaced the copyright text with SPDX tags.

Context regarding the copyright text changes:

• SPDX-LicenseIdentifier
• SPDX-FileTags