Preview plugin improvements

## Motivation ##
- Give clarity to similar asset access in different places
- Gather both the preview plugin and the image plugin in one single File Plugin

## Acceptance criteria ##
- [ ] List all the global files associated to the selected dataset
- [ ] Display two kinds of visual for two categories of files: images and files
- [ ] Being able to download one by one assets.
- [ ] Display the count of each file type
- [ ] All the user to download all the files as zip format.
- [ ] Allow pagination when we have large list of files

## Description ##
While testing the plugin after the last consolidation, a few feedback were collected:
1. Agreed plugin name when Alex did the initial design was "Assets"
2. Table header could be made clearer as follow:
a. Name
b. Encoding Format
c. File Size
d. Actions
3. The action buttons take a lot of space, could we consider a more compact representation with only icons in the buttons ? Tooltip would show the current labels (Download, Copy Location, Preview)
4. We shouldn't show paging if only one page is available

### Current plugin: ###

## Mockups ##
***Global view***

**Default**

**Selected**

**Edit mode**

**Add new file(s)**

**New file(s) component states**

No source files, tests, or entry points are named. Start by locating the current preview and image plugins and compare them with the supplied mockups; done means the listed asset views, file actions, counts, pagination, and naming changes are implemented.

Written by the indexing model from the issue text.