[APSTUD-8187] Added default values for UI elements

Taken from https://github.com/aptana/studio3-rcp/blob/development/plugins/com.aptana.editor.common.override/plugin.properties and https://github.com/aptana/studio3-rcp/blob/development/plugins/com.aptana.ui.override/OSGI-INF/l10n/bundle.properties

I believe this covers all the visible elements, but my search was not exhaustive. I went through the list of properties in the above two files, and then double-checked the UI. There could be some missing. Note that I did not add values for the  keyboard shortcut mnemonics. Doing so seemed to cause an error, but leaving it off appeared to have no impact.