Separate compilation and linker phases (#376)

Separate between compilation and linker phases to allow deploy time
linking and back-porting era compiler changes to fix #91. Unlinked
contract binaries (caused by missing libraries or missing factory
dependencies in turn) are emitted as raw ELF object.

Few drive by fixes:
- #98
- A compiler panic on missing libraries definitions.
- Fixes some incosistent type forwarding in JSON output (empty string
vs. null object).
- Remove the unused fallback for size optimization setting.
- Remove the broken `--lvm-ir`  mode.
- CI workflow fixes.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>

crates/common/src/contract_identifier.rs

@@ -0,0 +1,33 @@
+//! The contract identifier helper library.
+
+use serde::{Deserialize, Serialize};
+
+/// This structure simplifies passing the contract identifiers through the compilation pipeline.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ContractIdentifier {
+    /// The absolute file path.
+    pub path: String,
+    /// The contract name.
+    /// Is set for Solidity contracts only. Otherwise it would be equal to the file name.
+    pub name: Option<String>,
+    /// The full contract identifier.
+    /// For Solidity, The format is `<absolute file path>:<contract name>`.
+    /// For other languages, `<absolute file path>`.
+    pub full_path: String,
+}
+
+impl ContractIdentifier {
+    /// A shortcut constructor.
+    pub fn new(path: String, name: Option<String>) -> Self {
+        let full_path = match name {
+            Some(ref name) => format!("{path}:{name}"),
+            None => path.clone(),
+        };
+
+        Self {
+            path,
+            name,
+            full_path,
+        }
+    }
+}