Ignore all external events in the Profiler (vaadin#2951)

* Ignore all external events in the Profiler

Port changes from Fw 8.1.0.alpha6
Original PR:
vaadin/framework#9033

Add release dependency to POM for components (vaadin#2882)

add maven-release-plugin and deploy-plugin to POM;
add vaadin-prereleases (maven central repo);
remove unused repositories, as they are added to components;
remove dupulicated settings.

Update combobox webcomponent version to 3.0.1. Regenerate flow compon…

…ent and update bom. (vaadin#2827)

Add API for freezing grid columns (vaadin#2784)

Fix a bug when there more multiple elements with the same id in diffe…

…rent dom modules inside a bundled file. (vaadin#2714)

Update contribution instructions. (vaadin#2669)

Fix route string generation. (vaadin#2589)

Now generated routes never start or end with '/'

Do flush for every initial server side property (vaadin#2555)

Do flush after each property update. There may be several
properties and it looks like a property update may trigger
default values of other properties back.

Fixes vaadin#2304

Scope to provided instead of test. (vaadin#2525)

TeamCity release buildfail on javadoc not
finding javax.servlet.http.HttpSession

Change frontend paths defaults. (vaadin#2436)