Update Google Analytics logging

[pverscha]

Right now, logging actions to Google Analytics is still performed by using a script that's injected globally into the web page. A new package, however, exists for Vue that could make this process "cleaner": https://www.npmjs.com/package/vue-gtag.

Once we start to clean up the logging, I propose to log the following user actions (anonymously of course):

Single peptide analysis

• view matched proteins table
• view lineage tree
• view lineage table
• view GO-terms table
• view EC-numbers table
• view InterPro table

Multi peptide analysis

• load sample assay
• load PRIDE assay
• load local storage assay
• create assay
• download MPA results (CSV - Intl)
• download MPA results (CSV - EU)
• download MPA results (TSV)
• launch inter-assay comparison
• launch intra-assay comparison
• view sunburst
• view treemap
• view treeview
• view hierarchical outline
• view GO-terms table
• view EC-numbers table
• view InterPro table

General actions

• download image (SVG)
• download image (PNG)

A subset of these actions are already logged, but expanding this set might be valuable. This information helps us to improve our product and can help us to decide which features should be expanded / improved.