Update New Tab Page Images and refine design

[rossmoody]

Need to update the background images from Muon since we are now on Core. New tab page also needs some light polish surrounding icon style parity, typography standards and responsive formatting.

[srirambv]

Verification passed on

Brave	0.60.29 Chromium: 72.0.3626.96 (Official Build) beta(64-bit)
Revision	84098ee7ef8622a9defc2ef043cd8930b617b10e-refs/branch-heads/3626@{#836}
OS	Linux

• Verified all points from NTP Refinement brave-core#1091
• Encountered NTP images are stretched out but shows full image when dev tools are opened #3380 while verifying the issue

Verification passed on

Brave	0.60.29 Chromium: 72.0.3626.96 (Official Build) beta(64-bit)
Revision	84098ee7ef8622a9defc2ef043cd8930b617b10e-refs/branch-heads/3626@{#836}
OS	Windows 7

Used test plan from ttps://github.com/brave/brave-core/pull/1091

Verified passed with

Brave	0.60.28 Chromium: 72.0.3626.96 (Official Build) beta(64-bit)
Revision	84098ee7ef8622a9defc2ef043cd8930b617b10e-refs/branch-heads/3626@{#836}
OS	Mac OS X

• Verified items in NTP Refinement brave-core#1091
• Logged one new tab page image links to a site which is not secure #3384 , encountered Bookmark and pin icon behavior is not correct for top sites (on new tab page) #3347